ii.-ON THE gampsonychidj:, an undescribed family of fossil 



SCHIZOPOD CRUSTACEA. PL III, FIGS. 14 ; VII, FIGS. 1, 2. 



BEAD APRIL 21, 1855. 



By A. S. Packard. 



The opportunity of examining at my leisure about a dozen specimens of Palwoearis, typus of 

 Meek and Wortheu, kindly afforded me by Messrs. R. D. Lacoe and J. C. Carr, has enabled me to 

 work out some characters of this genus not mentioned by the original describers. The study of 

 these specimens has induced me to compare the genus with Gampsonyx, and the result has led to 

 the formation of a family or higher group for the genera, which should probably stand at the base 

 of the Schizopoda, while also serving to bridge over the chasm existing between the Thoracostra- 

 cous suborders, Syucarida and Schizopoda.' 



Palaeocaris was first described by Messrs. Meek and Wortben, in the Proceedings of the 

 Academy of Natural Sciences of Philadelphia (1865, p. 48), from specimens occurring in clay-stone 

 concretions in the lower part of tiie true coal measures, at Mazon Creek, Morris, Grundy County, 

 Illinois. Afterwards, in the third volume of the Reports of the Geological Survey of Illinois, 1868, 

 the same authors figured the fossil, and expressed themselves as follows regarding its afBuities: 

 "Hence it would seem to present something cf a combination of decapod (macrourau) and tetra- 

 decapod characters. That is, it possesses the caudal appendages, anteriorly directed thoracic legs, 

 the anteuuiB (some of the specimens appear, also, to show basal scales to the outer antennae) and 

 general aspect of a macrourau, with the distinct head, divided thorax (without a carapace), and seven 

 pairs of thoracic legs, of a tetradecapod. We have not been able to see its eyes, but from its other 

 decapod characters, and its analogy to Gampsonyx, which is said by von Meyer to have pedun- 

 culated, or at any rate movable, eyes, we are strongly inclined to believe that our fossil will be 

 found to agree with Gampsonyx in this character also. 



" It therefore became a matter of interest to determine to which of the subclasses, Decapoda or 

 Tetradecapoda, it really belongs. That it belongs rather near Gampsonyx, though not to the same 

 subordinate section (Schizopoda), there can be little doubt. Hence these two forms apparently fall 

 naturally into the same family. Professors Jordan and von Meyer seem to have regarded Gamp- 

 sonyx as a Tetradecapod, connected with the Amphipoda, but also possessing macroaral decapod 

 affinities. Professor Dana, however, regards it as a low type of Macrura, belonging to the section 

 Schizopoda. He and Dr. Stimpson, to whom we sent sketches of our better specimens of Palneo- 

 caris, concur in the opinion, judging from all its characters yet known, that it is a low embryonic 

 type of the Macrura, in which the carapace is not developed. 



■ 'We Lave not seen Burmoister's memoir "Ueber Gampsouyclms" (Abh. d. naturf. Ges. in Halle, ii, 191, 1855), 

 but Zittel (Handbucli der PaUeontologie, p. CTO) quotes Burmeister as stating that he regarded it ''as the representa- 

 tive of a special group of Crustacea, which unites in itself some of the most essential features in the organization of 

 the Stomapoda and Amphipoda." 



S. Mis. 154 17 129 



