154 A REVISION OF THE ASTACID^. 



been artificially introduced, according to Dr. Radde, 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^E. 



Abundant fossil remains of Crustacea nearly allied to the recent Homaridse and Asta- 

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

 and Wiirtemberg. These ancient Decapods, belonging to the genera Eryina 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 first pair large and powerful), 

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

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

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

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

 (agreeing in this regard with the telsou of the modern Homaridae and Parastacinse), and 

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

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

 the Astacidiu. If we unite the Honiarid;e and the Astacidffi in one tribe, the Astacoidea, 

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

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

 llomaridse and Astacidse of our seas and rivers. Unfortunately, these fossils have im- 

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

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

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

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

 the anterior abdominal appendages. In our ignorance of these structural characters in 

 these marine Jurassic fossils I cannot see the slightest ground for Huxley's conclusion, 

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

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

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

 spines on the penultimate segment of the fourth pair of legs. In P. j>ustuhsus (Miinst.) 

 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 Pseudastacus, as distinguished 

 from Eryma, approach the Astacidie of the preseut time. Boas* has called attention to 

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

 the anterior and more deeply impressed groove (marked d 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 Nephrops. 



* For au account of these animals, the reader is referred to the beautifully illustrated work of Oppel, 

 Palaeoutologische Milthrilimgon, Stuttgart, 1862. The Astacus Kaorrii of Milne Edwards (Hist. Nat. Crust., 

 II. 333), figured by Kuorr and by Desmarest, is probably an Eryma. 



f Huxley, The Crayfish, p. 313. 



t Studic'r over Decapodernes Slsegtskabsforhold. Vidensk. Selsk. Skr., 6te Rsekke, Naturvid. og Math. 

 Afd , Bd. I. pp. 71, 170, foot-note 2, 1880. 



