CAMBARUS. 3 



lack the bilobecl plaited lamina of the Potamobiinos, although the stem may 

 be expanded into a wing ; the epipodite of the first maxilliped almost 

 always carries branchial fdaments ; the coxopoditic setaj terminate in hooks; 

 the telson is not divided by a transverse suture.* 



Six genera of Parastacinae have been described ; viz. Astucoidcs, by Gue- 

 rin ; Cheraps and Engccua, by Erichson ; Panmq)hrops, by White ; 'Astacopsis 

 and Parastacus, by Huxley. Some of these genera are based on too tri\ial 

 characters to be valid. The group will be revised in the second part of this 

 memoir. 



CAMBAEUS. 



In the genus Cambarus, established by Erichson in 184G, t the cephalo- 

 thorax is subcylindrical. The last thoracic somite is devoid of gills, neither 

 are there any traces of rudimentary pleurobranchia3 on the anterior somites ; 

 the hindmost podobranchia has no lamina. The branchial formula is as 

 follows : — 



Somite. { PoDoituANcni.E. ARTiiRonRANCHi.E. Pleueobra.xciii.k. 



Anterior. Posterior. 



VI (cp.) . ... ... = (cp.) 



VII 1...1...0...0 = 2 



VIII 1...1...1...0 = 3 



IX 1 ... 1 ... 1 ... = 3 



X 1 ... 1 ... 1 ... = 3 



XI 1 ... 1 ... 1 ... = 3 



XII 1 ... 1 ... 1 ... = 3 



XIII ... ... ... = 



G + op. + G + 5 -f =17 + cp. 



This gives a total of thirty-four branchiae, counting those on both sides of 

 the thorax. The orifice of the green gland is situate near the apex of the 



» Cliilton (Trans. New Zealand Inst., Vol. XV. pp. 152, 103, PI. xx. %. 7, 1S82) has observed tliat 

 the internal male reprodiietive. organs in Punniephrops sdosiis are very different from those in the Potanio- 

 biinsE. In the former the testes are two long tubes united by a transverse cominissiirc, while iu the latter 

 they form a trilobcd organ through the coalescence of the right and left testes posterior to tlie vasa dcfcrcntia. 

 I have dissected an undcscribed Parastaeine from Chili, and find the testes to agree with those of Para- 

 nriphrops. It will probably be found that all the Parastacinae agree in tliis regard. On account of tiic resem- 

 blance of the internal male generative organs in Paranephrops and Paliuurus, and tlie furl her agreement of 

 the Parastaein.T and Palinnrid.'e in tlie absence of the first pair of abdominal ap])ciulagps and presence of 

 booked seta;, Chilton has forced these groups into too close rclationsliip. Cf. T. Jeffery Parker, iu the same 

 journal, Vol. XVI. p. 305. 



I Uebersicht der Artcu dcr Gattung Astaeus. .Vrcii. f. Naturgesch., XII. Jalirg., Bd. 1. p. SS. 



X The somite that bears the first pair of maxillipeds is here reckoned as the sixth. 



