134 Mr. J. Wood-Mason uu the Genus Deidamia. 



jilate brought to a point posteriorly ; its lateral plates oval, 

 almost equal in length to the former, tlie outer ones not divided 

 into two halves by a transverse line. Five pairs of abdominal 

 aj)])endages are present in the male ; those of the first segment 

 are slender, with a single spirally coiled terminal ])late ; on 

 the sueceeding ones two long, narrow, terminal ])latcs are 

 always present ; on the second, indeed, even a third aeeessoiy 

 inner plate is added ; the basilar joint is much elongated, but 

 gradually diminishes in length backwards. 



This species agrees in the general form of its body with the 

 Scyllarida^, from which, however, it is essentially distinguished 

 by the ditierent form of its antenna}, and by its didactyle legs, as 

 Avell as by its narrow sternum. With the Astacidaj it has 

 nothing in common, beyond the lamellar appendage at the 

 base of the outer antennae and the didactyle feet, but is in other 

 respects perfectly dilferent in structui-e from them. The genua 

 conforms most nearly to the fossil crayfish {Eryon Cuvierit) 

 from the Solenhofen Slates, described by Desmarest, in that 

 in this latter also a flattened cephalothorax, antennte, and legs 

 of similar structure are found ; the hind body, however, is in 

 that species much narrower than the cephalothorax, and the 

 lamellar appendage at the base of the outer antennaj much 

 enlarged. It forms with that extinct form a transitional group 

 between the Scyllaridaj (Loricata), on the one hand, and the 

 Astacida3 on the otlier. 



Polycheles tyjMops, C. Heller, 



Beitrage zur naheren Kenntniss der Macrouren, Sitzungsb. der 

 Akad. der Wiss. 1862, Bd. xlv. p. 392, Taf. i. f. 1-6. 



The cephalothorax of this species measures 10 lines in 

 length, in front 5, behind 5*4, and across the middle 6 lines in 

 breadth. The lateral margins are tolerably sharp and distinctly 

 toothed, especially towards the front, the lateral angles pro- 

 jecting, with their points directed forwards and outwards. 

 The flat upjier surface is divided by a distinct, anteriorly 

 concave cervical fuiTOW, into an anterior and posterior moiety, 

 the lateral extremities of the same bifrnxated outwards into 

 two branches running to the margins, and there enclosing a 

 triangular lateral area. Along the middle there runs from 

 before backwards a sharp toothed ridge ; another sliorter and 

 weaker longitudinal ridge is found on each side on the hinder 

 half of the cephalothorax, somewhat nearer to the lateral 

 margins than to the middle line. Towards the front on each 

 side lie fom- or five sharp teeth, one behind the other, in a 

 slightly curved, inwardly convex line ; in addition, the whole 



