356 EEPOET OF COMMISSIONER OP PISH AND PISHEEIES. 



spawning in May, but at Xew Haven they spawn as early as March and 

 April. It is probable that the period of spawning extends over several 

 months. Mr. Sanderson Smith thinks that they also spawn in autumn, 

 on Long Island. It is not known how long a time each female requires 

 for the formation of her string of capsules. There are two forms of these 

 capsules, about equally abundant in this region. In one the sides of 

 the capsules are nearly smooth, but the edge is thick or truncate along 

 most of the circumference, and crossed by numerous sharp transverse 

 ridges or partitions, dividing it into facets. Dr. Coues states that these 

 belong to F. carica. An examination of the young shells, ready to leave 

 the capsules, confirms this. The other kind has larger and thinner cap- 

 sules, with a thin, sharp outer edge, while the sides have radiating 

 ridges or raised lines. Sometimes the sides are unlike, one being smooth 

 and more or less concave, the other convex and crossed by ten or twelve 

 radiating, elevated ridges, extending to the edge. This kind was attrib- 

 uted to F. carica by Dr. G-. H. Perkins, and formerly by Mr. Sanderson 

 Smith, but a more careful examination of the young shells, within the 

 capsules, shows that they belong to S. canaliculata. 



Among the sand-dwelling bivalve shells we find quite a number of 

 species that burrow rapidly and deeply, some of them living in perma- 

 nent holes or perpendicular burrows, into which they can quickly de- 

 scend for safety, and others burrowing in the sand in all directions, 

 without permanent holes. 



The " razor-shell," Ensatella Americana. (Plate XXVI, fig. 182, and 

 Plate XXXII, fig. 245,) is a common inhabitant of sand-flats and sand- 

 bars, where the water is pure, generally living near low-water mark or 

 below, but sometimes found considerably above low-water mark, as on 

 the sand-bar at Savin Eock. This curious mollusk constructs a deep, 

 nearly round, somewhat permanent burrow, which descends nearly per- 

 pendicularly into the sand to the depth of two or three feet. These 

 holes can generally be recognized, by their large size and somewhat 

 elliptical form, when the tide is out. Sometimes they are very abundant 

 in certain spots and not found elsewhere in the neighborhood. They 

 sometimes come to the top of the burrow, when left by the tide, and pro- 

 ject an inch or two of the end of the shell above the surface of the sand ; 

 at such times, if cautiously approached, many can easily be secured by 

 pulling them out with a sudden jerk, but if the sand be jarred the whole 

 colony will usually take the altirm and instantly disappear. When thus 

 warned it is generally useless to attempt to dig them out, for they quickly 

 descend beyond the reach of the spade. They will often hold themselves 

 so firmly in their holes by means of the expanded end of the long mus- 

 cular foot, that the body may be drawn entirely out of the shell before 

 they will let go. When not visible at the orifice they can often be se- 

 cured by cutting off their retreat with a sudden oblique thrust of the 

 spade below them. They are obliged to come up to the upper part of 

 the burrow on account of the shortness of their siphons, or breathing- 



