32 FOSSIL MALACOSTRACOUS CRUSTACEA. 



Genus — Meyeri a, M' Cop, 



Char. Gen. Testa compressa, alta, pluri-carinata, rostrata ; sulco nuchali acute angu- 

 lari. Abdomen sernicylindricum, sculptum, processu laterali segmenti secundi lato, rotun- 

 dato. Cauda flabettum exterius transverse divisum. 



The genus Meyerla was established by Prof. M'Coy for the reception of two very 

 beautiful species, one of which is peculiar to the Speeton Clay, the other occurring in great 

 numbers in the lower Greensand of Atherfield, in the Isle of Wight. Its characters are 

 strongly marked, and the general aspect very peculiar. The carapace in each of the 

 species at present known is much compressed, very deep, and sharply and highly ridged 

 along the middle of the back ; it is marked with several, distinct carinse, those on the 

 portion anterior to the nuchal furrow (the cephalic arch), most strongly so; the nuchal fur- 

 row is deep, and in the form of a V., each half meeting the opposite one on the median 

 line in an acute angle; the sides of the posterior portion (the scapular arch), are very broad 

 and flat ; the rostrum is small and acute. The abdomen is in both species curiously but 

 diversely sculptured; the epimeral plates are rather large, that of the second segment 

 broad and rounded, the posterior ones trigonal and slightly curved. The exterior caudal 

 piece is divided at about one third from the extremity by a transverse joint, as in 

 the Astacidae in general, which is marked by a thin carina. The legs, judging from the 

 fragments which have hitherto been observed, are long and slender ; but at present nothing 

 is known as to the form of the terminal joint. 



Professor M'Coy placed this genus in the family Thallassinadae {Thallassiniens of 

 Milne Edwards), but, as I shall presently show, upon entirely mistaken grounds. The 

 genus to which he supposes it to be most nearly allied is Gebia, a fossorial form, of which 

 two species inhabit our coasts. The characters upon which M'Coy relies for the supposed 

 relation are the size of the abdomen and the compressed form of the carapace. In the 

 first place, however, these characters are by no means universal in the family in question, 

 nor are they absent in several other families. The size of the carapace alone would at 

 once put it out of the category, as in the fossorial group this is invariably small, and 

 generally round ; but there are other characters which positively associate it with the 

 Astacidae. The division across the exterior plate of the tail is an absolutely distinctive 

 character of the latter family, never occurring in the others ; the epimeral plates of the 

 abdominal segments are large in the present genus ; they do not exist in any of the 

 Thallassinadae. There can, therefore, be no doubt as to the association of Meyeria with 

 the Astacoid group, and it is remarkable that hitherto we are unacquainted with a single 

 Thallassinian form in our British rocks, although several well-marked species have been 

 found on the Continent, and have formed the subject of a very interesting and well- 

 elaborated paper by M. Adolphc Milne Edwards, which evinces a thorough know- 

 ledge of his subject, and a discrimination worthy of the distinguished name he bears. 



