Packard.] OOA [Feb. 5, 



The generic characters as drawn from the carapace alone are as follows : 

 Valves one half as long as broad ; moderately full and convex, with no 

 definite, straight hinge-margin. It differs from Ceratiocaris in the lack of 

 a long, straight hinge-margin, the dorsal edge being curved, and in the 

 lower edge not being thickened, while the posterior end is well rounded. 

 The anterior end of the valves is about half as wide as the posterior end, 

 and is oblique, the lower part of the edge being directed outwards. From 

 Aristozoe it differs in the lack of a definite hinge-margin, and in its 

 elongated oval valves ; from Nothozoe in its well defined narrow anterior 

 end, and well defined dorsal and ventral edges. 



As Mr. Scudder's genus Khachura* from the Carboniferous limestone of 

 Danville, Illinois, is only represented by the end of the abdomen, it is 

 impossible to discuss its relationship to that form. 



The specimen is a cast, and shows no tracings of markings on the exterior 

 of the valves. In form it is ovate, obliquely truncated at each end ; the 

 dorsal edge is not so much curved as the ventral edge, but it is more 

 curved towards the posterior edge than towards the anterior ; the ventral 

 edge is quite regularly curved. The anterior end is obliquely truncated, 

 the lower angle directed outwards. The posterior edge is about a third 

 wider than the anterior end, and is directed obliquely inwards so as to be 

 nearly parallel with the anterior end. While each end of the valves is 

 well preserved, the dorsal and ventral edges have apparently not been 

 preserved, as they are usually thickened in the other species of the genus. 



The lamellate limhs are situated in the specimen at the posterior end of 

 the carapace ; probably after death the carapace turned around and sepa- 

 rated from the body, which with the extremities became much displaced. 



Of the lamellate limbs there are traces of four pairs. They are broad 

 and thin, slightly contracted in width near the base, and at the distal 

 extremity quite regularly rounded, with the free ends apparently slightly 

 folded longitudinally, the edges appearing to be slightly crenulated, but 



Fig. 3.— Outline of O'yptozoe problcmalicus, showing the shape of the lamelJate 

 feet, the valve being upside down. 



these folds were perhaps due to changes after death. All the feet are of 

 nearly the same size. They are about two thirds as long as the carapace 



*Proc. Bost. Soc. Nat. Hist, xix, 1878, PI. 8, Fig. 3, 3a. 



