570 Contributions to Invertebrate Palseonlology. 



Genus PAL^OPAL^MOX Whitfield. 

 Am. Jour. Arts and Sci., 3d series, vol. 19, p. 40, 1880. 



A macrouran decapod crustacean, having a shrimp-like body, with a thoracic 

 carapace narrowed but not rostrate in front, and keeled on the back and sides. 

 Abdomen of six segments terminated by an elongated triangular and pointed 

 telson ; segments arched, pleura smooth, not expanded nor lobed, their ex- 

 tremities rounded. Sixth segment bearing caudal flaps, one on each side, 

 composed of five visible elements, the outer four apparently anculosed to form 

 a single large triangular plate on each side of the telson. Thoracic ambula- 

 tory appendages elongated, smooth, and filiform, except the upper (second) 

 joint, which is laterally compressed. Abdominal appendages short, the upper 

 joints flattened or convex anteriorly, as if for the attachment of plates or 

 fimbriae. Antennfe with the basal joints strong and well developed, of large 

 size, much exceeding in strength any of the thoracic limbs. Eye peduncles 

 short. 



This is so far as I am aware the most ancient decapod crustacean 

 yet recognized, and on that account alone is of great interest. The 

 character of the caudal plates, in having the parts combined to form 

 a solid plate on each side of the telson, is also an interesting feature, 

 if rightly understood. From the impression of the plate as seen on 

 the ventral side, it was at first supposed to be of a simple element 

 only, but on obtaining an impression in the fragment of rock, chip- 

 ped from the top or dorsal surface, the obscure lines of the first and 

 second joints were detected, while the outer three are only traceable 

 from the very slight difference in the surface character of two of 

 them, and the thickened substance of the third or marginal one. Of 

 the thoracic limbs only parts have been seen, and of the abdominal 

 members the three anterior ones on one side ; the others being con- 

 cealed by the rock. The eye-stalks appear to have been very short, 

 judging from the spherical cavities beneath the anterior extremity 

 of the carapace, which are small, close together, and shallow. 



The earliest form of decapod crustacean previously described, so 

 far as I can ascertain, is given by Mr. Salter in the Quart. Jour. 

 Geol. Soc. London, vol. 17, j). 531, ISOl, as Palseocrangon social e ; 

 said to be from the Lower Carboniferous limestone of Fifeshire, 

 Scotland. There is another su])pos{'d decapod, Gitocrangov, noticed 

 by Richter (JJeitriige Pal-.eont. Thiring.) from the Upper Devonian, 

 which is mentioned by Salter; but of which he says he is doubtful 

 if it be a crustacean at all. I have not seen the work in which the 

 original description occurs, and can only judge of its nature from 

 Mr. Salter's remarks. 



