236 ANNALS NEW YORK ACADEMY OF SCIENCES 



Amphissites rugosus sp. nov. 



Shell small, subquadrate, with the two ends nearly symmetrically formed, 

 so that it is difficult to distinguish which is anterior and which posterior. 

 The dorsal and ventral margins are straight and parallel. The ventral is 

 curved upward at the ends, which are regularly rounded ; the posterior is 

 slightly oblique and projecting. Cardinal angles rounded. 



The convexity is rather high, developed especially about the margins. The 

 surface is modified in a rather complicated manner, there being four flanges 

 or ridges, while the median portion of the side is occupied by a large Icnob 

 or boss. The margins of the base and sides are slightly thickened and pro- 

 jecting, making what may be called the first flange. The second is just above, 

 separated by a narrow, deep groove, and it projects beyond the true margin. 

 The third lies considerably within the second and does not conform to it, 

 since a broader space is left at the inferior angles (especially the anterior 

 one) than along the ventral border, while it meets the dorsal margin at the 

 cardinal angles. The fourth flange or ridge is less distinct than the others, 

 tending to become obsolete ventrally, becoming much thiclcer and more ele- 

 vated anteriorly, so that where it terminates abruptly at the dorsal border, it 

 forms in the cardinal view a large flat triangular area. The median pit is 

 small and situated just below the inflated umbonate median portion of the 

 shell. The surface is finely reticulated, except along the flanges, which are 

 dense and smooth. 



Glyptopleura gen. nov. 



Shell rather small, subquadrate. with a backward swing, the posterior end 

 being higher than the anterior and somewhat truncated. Inequivalve ; the 

 left valve is much the larger and overlaps the other all around save along 

 the distinct straight binge. There is a subcentral pit. The surface is marked 

 by inosculating costse. 



Type. — Glyptopleura mopinata. 



This type has the general appearance of certain species referred to 

 KirJihya, hut it is distinguished from Kirl'hya by the fact that the left 

 valve is larger than the right — the reverse of Kirl'hya — and that it over- 

 laps the right strongly and throughout the circumference save along the 

 hinge. This difference, of course, depends partly upon the orientation of 

 the shell. In the Beyrichiidas and in Kirl-hya itself, the shape is sub- 

 rhomboidal, and the higher, truncated, more projecting end is called the 

 posterior. If the same criteria are applied to tlie present species, the left 

 valve is the larger and overlaps the right as described above. In tbe 

 contrary interpretation, the overlapping of the valves in the present shell 

 would more nearly correspond with Kirl'hya. though more pronounced, 

 but the other data of orientation would be reversed. It seems to l^e more 

 probable that the configuration is the same as in Kirl'hya and the Boy- 

 richias. 



