No.2.] PACKARD ON TERTIARY CRAYFISH. 395 



tennse is longer than in living Astaci or Cambari. The rostrum of A. 

 hreviforcej^s is very long and acute. 



C. primcevus differs from Astacus breviforceps in the narrower chela, 

 and in the larger tubercles of the surface. It differs from A. chenoderma 

 in the different shape of the large chelse, those of A. chenoderma being 

 flatter and thinner, while the ornamentation or sculpturing is also 

 different, the tubercles of the carapace and limbs being higher and more 

 prominent in G. primcevus than in either of the two Idaho species exam- 

 ined by me. 



The Idaho Astaci being probably of more recent age than the Mio- 

 cene, the Gambarus primwvus is exceedingly interesting, from the fact 

 that it represents a period in which heretofore no fossil crayfish has 

 been found. The soft, fine, fissile, clayey shales of the Bear Eiver ter- 

 tiaries contain not only a good many herring-like fish, but also genuine 

 skates. The presence of land plants mingled with marine animals, 

 shows that the waters were fresh, but communicated with the sea ; the 

 conditions were apparently those of a deep estuary into which fresh 

 water streams ran, and in these rivers lived the crayfish. The deposits 

 were probably Eocene, if these divisions are to be retained for the Ter- 

 tiary deposits of the West, and may have been laid down nearer the 

 ocean than those of Green Eiver. At any rate, it is safe to say that the 

 Gambarus primcevus existed in the Bear Eiver basin in early Tertiary 

 times (the Green Eiver epoch), while the Idaho Astaci were of much 

 later age, possibly of so-called Pliocene or the transition period which 

 connected the Tertiary with the Quaternary period. The Gambarus 

 primcevus may therefore be regarded as probably an Eocene crayfish. 



It thus appears that there is a tolerably complete set of forms of the 

 modern type of crayfish, beginning with the Cretaceous period and ex- 

 tending through the Lower and Upper Tertiary, and culminating in the 

 present assemblage of Astaci and Gambari, with allied forms peopling 

 the cooler parts of the northern hemisphere. 



It was the intention of the writer to examine into the geological suc- 

 cession of the crayfishes, but since the specimens were received for exam- 

 ination the excellent and thorough work of Professor Huxley, entitled 

 " The Crayfish," has appeared, and his inquiries into the geological suc- 

 cession and probable genealogy of the existing crayfish completely cover 

 the ground. We will condense the statements of Professor Huxley, in 

 order that the reader may see the interest to be attached to the discovery 

 of the Wyoming fossils. 



While the shrimps or Macrura date back to the Carboniferous, being 

 there represented by Anthrapaltemon, with, however, no special atfini- 

 ties to the Astaci, it is not until we ascend to the Middle Lias and strata 

 belonging near the top of the Jurassic series that we find in the genus 

 Eryma, of which some forty species have been recognized, a genus which 

 is closely allied to Astacus and Gambarus. It was, however, a marine 

 form, and no fresh- water types existed in the fresh-water beds of the 



