[Jordan and Evermann, 1896-1900, p. 2107.]
Perhaps the most noticeable character of this and of the striped sea snail (p. 466) is that it is shaped more like a tadpole than like the conventional fish, thanks to the cylindrical fore part of the trunk, together with the broad rounded snout and fat soft belly, and the abrupt flattening (sidewise) of the body close behind the vent. It is also provided with a sucking disk similar to that of the lumpfish (p. 459). In side view the body is deepest abreast the pectoral fins (about four times as long as it is deep, not counting the caudal fin), tapering evenly to a moderate caudal peduncle. The head is flat above, the mouth is at the tip of the snout and moderately wide, and the jaws are armed with many small teeth arranged in bands.
The dorsal fin (6 spines and 26 soft rays) originates close behind the pectorals and runs continuously to the base of the caudal though it is separate from the latter. The dorsal spines are longer in males than in females, and project further beyond the membrane, giving the fin a fringed appearance. The anal fin (23 to 27 rays) originates under or a little behind the origin of the soft portion of the dorsal fin to which it corresponds in size, and outline. The pectoral fins are not only very large and fanlike, but their bases run forward under the throat, where they expand into secondary lobes or wings with fringed edges. The ventral fins appear only as a circle of low knobs in the center of the sucking disk, which is situated on the throat between the pectoral fins. The skin is scaleless, and it is smooth except at spawning time, when the male becomes rough with small prickles.[page 465]
Olive to reddish brown with lighter and darker cloudings and dots, the dorsal and anal fins often with crossbars. Its tints vary widely, also its markings and the strength of coloration, whether pale or dark, as is the case with so many fishes that live on the bottom.
Maximum length about 5 inches.
This sea snail resembles the following species (p. 466) so closely that the two are likely to be confused. The most evident difference between them is that the spiny portion of the dorsal (6 spines hardly stiffer than the soft rays) is marked off from the much longer soft part (22 to 27 rays) by a slight notch in the present species, whereas there is no such separation in the striped sea snail.
Sea snails are inconspicuous little fish, usually found coiled up (tail to head) under stones, or attached by the sucker to some kelp stalk or other seaweed. But sometimes they swim to the upper water layers: thus the Halcyon specimens, for instance, mentioned below, were taken in a tow net at 8 fathoms, where the water was about 22 fathoms deep. And they seem to be indifferent to depth within moderate limits, for while they have been dredged as deep as 50 fathoms at various localities in our Gulf, they are often found clinging to lobster pots in the Bay of Fundy, (p. 465), while they have been taken in only a few feet of water in Massachusetts Bay. One was even found in a tide pool near St. Andrews, in Passamaquoddy Bay So it would not be astonishing to find sea snails left in rock pools elsewhere, or on pebbly beaches by the ebbing tide, as often happens with its European representative. Young ones have been found living within the shells of the giant scallop (Pecten magellanicus), a curious habit that they share with the striped sea snail (p. 466) and with the hakes of the genus Urophycis (p. 224). Little else is known of the life of this sea snail, except that it is supposed to work inshore in winter to spawn. Presumably it feeds chiefly on small crustaceans and on small shellfish as its European relative does.
The spawning of this species has not been observed, but probably it takes place from March until midsummer in our Gulf, for Huntsman found larvae in Passamaquoddy Bay as early as April, while we towed one only 7 mm. long on German Bank as late as September 2 (1915).
The developmental stages of our sea snail have not been seen. The eggs of the European sea snail, which are about 1.1 mm. in diameter, and pale straw color to light salmon pink, sink and stick together, also to hydroids, seaweeds, and to debris of any kind. The little clusters are often brought up on long lines from 4 to 30 fathoms, but are sometimes found close below tide mark. There is no reason to suppose that the males care for the eggs, and the latter are so hardy that they do not suffer from exposure to the air for hours. Judging from the dates when newly hatched larvae have been seen, incubation of the European species occupies a month, perhaps longer in the case of the eggs that are spawned earliest in the season, at winter temperatures. The larvae are about 3.3 to 4.5 mm. long at hatching, with a small rose-red yolk sac that contains a large oil globule and that is inclosed in a net of blood vessels. Most of the characters of the adult are apparent at 11 to 12 mm. length, but the pectoral fins are brilliantly pigmented with yellow and black throughout the larval stage.
Rocky shores along the North American Coast from northeastern Newfoundland, the northern part of the Gulf of St. Lawrence and the Grand Banks to southern New England. It is rare west and south of Cape Cod, but has been taken at Woods Hole, on the coast of Connecticut, and off New Jersey.
This sea snail is generally distributed around the shore line of the Gulf. Thus the Halcyon trawled it off Yarmouth, Nova Scotia, in January 1921; it is rather common (according to Huntsman) in the Bay of Fundy and in Passamaquoddy Bay; and it has been definitely reported at Grand Manan; Eastport; Seguin Island; off Portland (where many have been collected); off Cape Elizabeth; at Kittery; and at various localities about Massachusetts Bay. It [page 466] has been taken on Georges Bank also, and on Browns, living in scallop shells (p. 465).
Vladykov and McKenzie characterize it as "not uncommon" all around Nova Scotia; it is classed by Huntsman as characteristic of the icy cold water on the banks in the southern part of the Gulf of St. Lawrence; and it has been reported from the estuary of the St. Lawrence River; from the northeastern part of the Gulf of St. Lawrence; off the south coast of Newfoundland; on the Grand Banks, and as far north on the Atlantic coast as the entrance to the Strait of Belle Isle.
 McKenzie and Homans, Proc. Nova Scotian Inst. Sci., vol. 19, Pt. 3, 1938, p. 278.
 McIntosh and Mastermann (Life histories of the British Marine Foodfishes, 1897 p. 191, pl. 2. fig. 9, 10) and Ehrenbaum (Nordisches Plankton, vol. 1, 1905-1909, p. 109) give descriptions of the eggs and larvae of the European sea snail N. montagui (as Cyclogaster montagui) from which the preceding is condensed.
 This fish is so closely allied to the north European sea snail, N. montagui (from which, however, it is quite distinct) that it passed under that name prior to 1898.
 A specimen was taken by Albatross II, off Atlantic City, lat. 39° 24' N., long. 74° 05' W., in 11 fathoms, in April 1930.
 Proc. Nova Scotian Inst. Sci., vol. 19, 1935, p. 99.
 From the trawlings of the Newfoundland Fisheries Research Commission.