I.—ON THE GAMPSONYCHIDA, AN UNDESCRIBED FAMILY OF FOSSIL 
SCHIZOPOD CRUSTACEA. PL. TU, FIGS. 1-4; VIL, FIGS. 1, 2. 
READ APRIL 21, 1855. 
By A. S. PACKARD. 
The opportunity of examining at my leisure about a dozen specimens of Palcocaris typus of 
Meek and Worthen, 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, Synearida and Schizopoda. ! 
Paleocaris was first described by Messrs. Meek and Worthen, 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 the true coal measures, at Mazon Creek, Morris, Grundy County, 
Illinois. Afterwards,in the third volume of the Reports of the Geological Survey of Tlinois, 1868, 
the same authors figured the fossil, and expressed themselves as follows regarding its affinities: 
“Hence it would seem to present something of a combination of decapod (macrouran) and tetra- 
decapod characters. That is, it possesses the caudal appendages, anteriorly directed thoracic legs, 
the antenne (some of the specimens appear, also, to show basal scales to the outer antenna) and 
general aspect of a macrouran, 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. 
“Tt 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 seein to have regarded Gamp- 
sonyx as a Tetradecapod, connected with the Amphipoda, but also possessing macroural decapod 
aftinities. 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 Paleo- 
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. 
1 We have not seen Burmeister’s memoir ‘‘ Ueber Gampsonychus” (Abh. d. naturf. Ges. in Halle, ii, LOL, 1855), 
but Zittel (Handbuch der Paleontologie, p. 670) 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 
