872 R. ETHERIDGE, JUN., ON THE OCCURRENCE OF k 



a depressed hemispherical body, having an externally granulated 

 shell, under the name of Hemitrochiscus paradoxus *. He was un- 

 able to state any thing definite as to the affinities of the fossil, but 

 provisionally regards it as the shell of a Crustacean from the Zech- 

 stein dolomite of Porsneek. 



1861. Dr. H. B. Geinitz refigured Hemitrochiscus paradoxus, 

 Schaur., and referred it to the Decapoda Brachyura f. His figures 

 aro much more intelligible than Schauroth's. Geinitz likewise de- 

 scribes PaloBOorangon (Prosopoaiscus) problematic us, Schaur., and 

 refers it to the Isopoda. He adopted the generic name Prosopo- 

 niscus, Kirkby, in preference to Palceocrangon, Schaur., apparently 

 without any very well-defined grounds ; but at the same time he re- 

 marks that Palceosphceroma would have been a more appropriate 

 name than either of the foregoing J. 



1871. Mr. F. B. Meek published a paper in the Proceedings of the 

 Academy of Natural Sciences of Philadelphia for this year, in which 

 he established the provisional genus Archceocaris for a shrimp-like 

 form of doubtful affinities §. Prof. Dana considered that it had 

 some relation with the recent genus Cuma. Prom the Waverly 

 group, Danville, Kentucky. 



1875. In the second volume of the Ohio Geological- Survey Re- 

 port, Archceocaris vermiformis is figured ||. It is referred to the 

 Tetradecapoda. 



The following Table (p. 873) will show at a glance the genera 

 enumerated in the foregoing bibliography, their authors, orders, geo- 

 logical horizons, and chief localities. 



3. Description of the Specimen. 



The remains of this interesting Crustacean are scanty in the 

 extreme. We at present possess only those of two individuals, one 

 of which is a film-like impression and its counterpart, compressed 

 laterally (figs. 1 & 2) ; and the other is a portion of the carapace 

 and body-segments of another individual flattened from above down- 

 wards (fig. 3), both in the same ironstone nodule. 



The more perfect of these, that seen in profile (PL XXVII. figs. 1 

 & 2), measured as nearly as possible 7 lines long by 3^ wide, taken 

 across the carapace. The length of the carapace is equal to, if not 

 somewhat greater than, that of the abdominal somites. The latter 

 are narrow and probably six in number (a, figs. 1 & 2), irrespective 

 of the telson (6, figs. 1 & 2). The thoracic appendages are certainly 

 six, and, if I mistake not, seven in number (c, figs. 1 & 2) ; but any 

 abdominal appendages that may have existed have quite disap- 

 peared. The telson and its caudal appendages (b, figs. 1 & 2) were 

 evidently a well-marked feature in the organism. 



To enter more minutely into the structure of this Crustacean, it 

 may be observed that the carapace is somewhat elongately quadran- 



* Zeitsehr. deutsch. geol. Gesellschaft, vi. p. 558. 



t Dyas, oder die Zechsteinformation unci das Rotbliogende, p. 28. 



\ P." 29. § P. 355. || T. 18. f. 7. 



