17 



The shape in general is oval. The dorsal margin is high, 

 arched, sloping steeply toward the posterior margin, with which it 

 forms a sharp angle, almost a tooth. The posterior margin is 

 short, straight, and has seven or eight teeth. Of these, the first 

 tipper tooth points obliquely upwards, the succeeding two also 

 upwards, though less steeply, and the rest either outward or 

 slightly downwards. The posterior margin joins the ventral in a 

 rounded angle. The ventral margin is concave, and has some- 

 what sparse, abundantly plumose, setas. The forward margin is 

 •strongly convex, and has numerous small teeth on its lower half. 

 These point downward or backward. The valves are marked 

 •by striae, which are very plain around the edges. At the upper 

 part of the posterior margin they are parallel to the back, grad- 

 xially changing their course so as to become perpendicular to the 

 ventral margin about its center. The succeeding striae incline 

 backward, and become at last parallel to the anterior margin. 

 There is an area in the center of the valves which is either ob- 

 scurely reticulated or smooth. The rostrum is long, stout, and 

 abruptly bent outwards into a hook at its tip. The post-abdo- 

 men is long, laterally compressed, truncated, with a dorsal row of 

 teeth, consisting of a cluster of four or five stout and long spines 

 at the lower corner, and eight or ten teeth following these, ar- 

 ranged somewhat in pairs. In this and all other cases of a dorsal 

 row of teeth, which I have seen, except in Eurycercus, the teeth are 

 not exactly on the dorsal margin of the post-abdomen, but are 

 set on the sides, usually each alternate tooth on the same side, so 

 that there are really two rows of teeth. The keel of the labrum 

 is somewhat tongue-shaped, running into a long, rounded projec- 

 tion behind. The ephippium forms on the rear upper part of the 

 shell. It contains one egg. Two summer eggs are produced at 

 one time. The color is yellowish, but remarkably transparent. 

 The male was not seen. 



Grlacialis, Cambridge, Mass., two specimens, 1875. Southamp- 

 ton, Mass., 1878; common. Madison, "Wis., July and August, 

 1877 ; common. 



The teeth on the posterior and anterior margins of shell at once 

 distinguish this species from all others with recurved rostrum. It 



