72 SIXTEENTH REPORT ON THE CABINET OF NAT. HISTORY. 



and is referable to a very distinct species, and perhaps to a distinct but 

 allied genus. 



2'^^^. The other specimens are from the Genesee slate, and consist of a 

 small specimen preserving two joints of the abdomen and a part of the tail- 

 appendages of a Geratiocaris, together with numerous specimens of the 

 detached caudal appendages which are sometimes thickly scattered over the 

 surface of the laminae. These specimens, in one locality, indicate the former 

 existence of great numbers of these animals ; but unfortunately they are so 

 macerated and compressed, that their examination affords very unsatisfac- 

 tory results. 



^^'^. A large slab from the Hamilton group, obtained many years since 

 from Otsego county by Mr. Sims, and now in the State Museum. On the 

 surface of this slab are the impressions and remains of the tail-joint and 

 appendages of at least four individuals of a large species of Dithyrocaris. 

 The fifth impression may have been of a displaced portion of one side of 

 the others, since the stone is so broken as to have lost the greater portion 

 of one side of one specimen. 



GENUS CEPvATIOCARIS (M'Coy). 

 CERATIOCAKIS ARMATUS ( n. s.). 



PLATE I. FIGS. 1, 2, 3. 



A fragment consisting of the three posterior joints of the ab- 

 domen and a part of the next anterior or second joint, together 

 with the triple spine of the tail. These articulations are somewhat 

 slender but strong, thickened at their anterior articulating edge 

 upon the back, while the dorsal posterior margin is thickened and 

 furnished with four strong short curved spines projecting over and 

 protecting' the joint : the second or most anterior articulation has 

 three spines on each side of the centre. On the under surface (the 

 fragment being nearly straight), the crustaceous articulating faces 

 are widely separated ; the posterior margin thickened and curved 

 outwards for the reception of the anterior callosity, showing an 

 arrangement for extreme flexure or incurving of the body. The 

 last joint is short and stout, broader in the middle than the next 

 anterior one. The central portion beconaes subangular, and is ex- 

 tended in a strong spine. On each side of the base of this spine, 

 it is depressed ; the lateral portions, becoming expanded, are 

 obliquely truncated behind, and to these faces the lateral spines 

 are articulated. The lower surface is nearly flat, slightly concave 

 in the middle, and the anterior margin elevated in a strong con- 

 dyle. The lateral spines are somewhat flattened and grooved 

 below, ,^nd abruptly rounded above. The form of the lower part 



