154 A REVISION OF THE ASTACID^. 



been artificially introduced, according to Dr. Raddc, into some of the tribu- 

 taries of the upper Koor (the Cyrus of the ancients), which flows eastward 

 into the Caspian Sea (Kessler). 



NOTE ON THE FOSSIL ASTACID^. 



AbniiJant fossil remains of Crustacea nearly allied to the recent Homarida? and Asta- 

 cidae are found in the Jurassic from the Middle Lias to tlie lithographic slates of Bavaria 

 and Wiirtemberg. These ancient Decapods, belonging to the genera Eryma and Pseudas- 

 tacus * agreed with the lobsters and crayfishes of the present day in having the three 

 anterior pairs of legs terminated by pincer-like claws (the tlrst pair large and powerful), 

 tlie abdominal pleura drawn out into prominent lateral plates, and the outer branch of 

 the enlarged posterior pair of appendages or swinunerets divided by a transverse suture. 

 The carapace was produced into a prominent rostrum, commonly denticulate on the 

 margin ; the telson sliowed no trace of a division into two pieces by a transverse suture 

 (ncfreeing in this regard with the telson of the modern l[oniarid;e and Parastacin»), and 

 was more triangular in outline than in the living forms; the large cheUe were nearly sym- 

 metrical on the two sides of the body, and the shell granulated or tuberculated, as in 

 tlie AstacidiU. If we unite the Homaridte and the Astacidre in one tribe, the Astacoidea, 

 there can be no reasonable doubt that tlie Jurassic genera Eryma and Pseudastacus would 

 be included properly in this tribe. To them we turn in seeking the progenitors of the 

 llomaridre and Astacidoe of our seas and rivers. Unfortunately, these fossils have im- 

 jmrted as yet no information concerning certain important structural features which must 

 be known before we can determine whether the Astaciue type was thus early differen- 

 tiated from the Homarine. I refer to the number, structure, and arrangement of the 

 gills ; tlie condition of the last thoracic somite, whetiier free or fixed ; and the structure of 

 the anterior abdoii;inal appendages. In our ignorance of these structural characters in 

 these marine Jurassic fossils I cannot see the slightest ground for Hu.x'ley's conclusion, 

 that in tlie genus Pseudastacus we already see a differentiation of the Astacine from the 

 Homarine type represented by Eryma. f Pseudastacus differs from Ei-yma in having a 

 longer rostrum, longer and thicker autennal peduncle and scale, and in the lack of movable 

 spines on the penultimate segment of the fourth pair of legs. In P. pustulusus (I\Iiinst.) 

 the inner as well as the outer branch of the swimmerets seems to have been divided by a 

 transverse suture. Now, in none of these particulars does P.seudastacus, as distinguished 

 from Eryma, approach the AstacidiTj of the present time. l>oiis:!: has called attention to 

 the fact that tlie transverse part of the " cervical " groove of Pseudastacus is tlie .same as 

 the anterior and more deeply impressed groove (marked </ in Boas's figures) on the cara- 

 pace of Eryma, and that it is not homologous with the cervical groove of Homarus and ^ 

 Astacus (c of Boas's figures), but rather with the anterior slightly impressed groove seen 

 on the carapace of Neplirops. 



* For au accnuut of tliese animals, the reader is referred to the beautifully illustrated work of Oppel, 

 Palaeontologische Miltheilungen, Stuttgart, 1S62. The Asfnc//x Knorrii of Mihie Edwards (Hist. Nat. Crust., 

 II. 333), figured by Knorr aud by Dcsmarcst, is probably au Eryma. 



t Huxley, The Crayfish, p. 343. 



X Studier over Decapodenies SlEegtskabsforhold. Vidensk. Selsk. Skr., 6te Rajkke, Naturvid. og Math. 

 Afd., Bd. I. pp. 7i, 170, foot-uote 2, 1S80. 



