154 A REVISION OF THE ASTACID2E. 



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 ASTACIDJ3. 



Abundant fossil remains of Crustacea nearly allied to the recent Homaridae 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 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 first pair large and powerful), 

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

 the enlarged posterior pair of appendages or swinnnerets 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 telson of the modern Homaridae and Parastacinee), and 

 was mure triangular in outline than in the living forms; the large chelae were nearly sym- 

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

 the AstaciiUe, If we unite the Homaridae and the Astacida3 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 

 Homaridffi and Astacidae 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 iu 

 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. t 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. pustidosus (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 Astacidae of the present time. Boasj 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 /in Boas's figures, on the cara- 

 pace of Eryma, and that it is not homologous witli the cervical groove of Romania and 

 Astacus {<■ of Boas's figures), but rather with the anterior slightly impressed groove seen 

 on the carapace of Nephrops. 



* For an account, of these animals, the render is referred to the beautifully illustrated work bfOppel, 

 Palaeontologische Mittheilungen, Stuttgart, L862. The d»tacu* Kuorrii of Milne Edwards (Hist. Nal ( rusl . 

 II. 333), figured by Knorrand by Desmarest, i- probably an Eryma. 



t Huxley, 'the Crayfish, p ' I 



| Studier ever Deeapodernea Slsgtskabsforhold. Vi.Inisk. Sclsk. Skr., Gte Rrckke, Naturvid, og Math. 

 Afd, lid I pp ; I. L76 fool note 2, L880. 



