No. 2.] PACKARD ON TEETIARY CRAYFISH. 393 



end (carpopodite) appears to be somewhat shorter than in Camharus. 

 Length of chela in the larger example (partly estimated) 19™'" ; breadth, 

 gmm. length of carpopodite, 5™'"; breadth, G™"'; meropodite, lO'"""; 

 breadth, Gf"^'". 



The other pairs of legs are moderately stout and heavily tuberculated 

 and spined, more so than even in large adult specimens of Astacus fiu- 

 viatiUs, which is more coarsely tuberculated than in any species of Cam- 

 harus which we have seen. 



Abdomen. — Of the usual proportion, but the surface is rougher than 

 usual, more so than in Astacus Jiuviatilis. The telson and the four rami 

 of the last pair of abdominal legs are of the same proportions and spined 

 in the same manner as in Camharus; the lateral spines of the telson are 

 stout, proportionately more so than in a specimen of C. affinis twice its 

 size. The shape of the broad rami is the same as in most, if not all, the 

 species of Camharus; the straight line of small spines near the end of the 

 exopodite being well marked. Length of abdomen in the small speci- 

 men, 18™™; breadth of the third segment, 9^-™™; length of telson, 4™'"; 

 breadth at base, 4™™. No traces of the abdominal appendages (except 

 the last pair just described) are to be seen. 



As to the generic relationship of this species we must remain in doubt 

 until the discovery of additional specimens enables us to determine the 

 number of branchiae, the species of Astacus having eighteen, and that of 

 Camharus having seventeen, the last pleurobranchia wanting in the latter 

 genus. 



The species of Camharus^ as is well known, are not found west of the 

 Eocky Mountains, the genus on the Pacific coast being replaced by Asta- 

 cus, thus presenting an interesting analogy to the European fauna. IS'ow 

 whether the Green Eiver and Bear Lake beds contained a fauna more 

 analogous to the Atlantic or Pacific slope is as yet unknown. 



However, judging from the form of the scape of the second antennae, 

 the tertiary species in question is apj)arently more closely allied to Cam- 

 harus than to Astacus, though the first pair of legs are rather shorter and 

 stou^^er than in Camharus, and the body more coarsely tuberculated, while 

 in the large numerous tubercles it resembles Astacus. 



Of all the species of Camharus, judging by our specimens and the fig- 

 ures in Hagen's Monograph; in the shape of the rostrum, the form of 

 the chelra and antenual scale it approaches most closely to Camharus 

 affinis. This is an interesting point, since it is evident, as Mv. Uhler 

 originally pointed out to us, and as we think seems quite evident, that G. 

 affinis is the most generalized species of all our crayfishes, being appar- 

 ently the ancestral form from which the other American species have 

 descended or been thrown off. 



We may in this connection refer to the three fossil forms from Idaho 

 Territory, described* by Prof. E. D. Cope, who has kindly allowed us to 

 examine his type specimens (those of A. suhc/rundiaUs excepted), which 



* Proceedings Amer. Phil. Soc, 1870, p. 605, vol. xi, No. 85. 



