94 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



The recent species of the genus to which the fossil belongs, 

 Thalassina scorpioides, is stated by Leach*, Desmarest f, and others, 

 to be a native of the Indian seas. Milne Edwards on the other 

 hand gives the coast of Chili as its habitat. It is not impossible 

 that it may have been found in both these localities ; a specimen 

 which I have in my possession was said to have been brought from 

 India, but of this I have no positive evidence. 



The fossil, which I propose to designate, after its discoverer, 

 Thalassina Emerii, consists of the sides of the carapace, in toler- 

 able preservation, the dorsal portion being quite lost ; the first four 

 joints of the first and second pairs of legs are tolerably perfect ; of 

 the third and fourth pairs the basal joints alone remain, and the 

 fifth pair is lost. The whole of the abdomen, with the exception of 

 the third segment, is very perfect ; it is abruptly bent forward upon 

 itself, the terminal joint resting beneath the thorax, between the third 

 and fourth pairs of legs {Jig- a). The rostrum also is very perfect, 

 broken off from the carapace, and lying vertically between the an- 

 terior legs (Jig. c). It is prolonged into a grooved triangular tooth, 

 and there is a small prominent tubercle on each side, at a short dis- 

 tance from it. The raised lines, circumscribing the rostral tooth, 

 are continued backwards to some distance, as is also its deep me- 

 dian groove. A second raised line is continued backwards from 

 the small denticle, or tubercle, on each side. 



The similarity between this species, as far as the state of the 

 fossil will allow of the comparison, and the recent one, is so great, 

 that there is some difficulty in fixing upon valid distinguishing 

 characters. It differs, however, in the proportion of the epimeral 

 or lateral portions of the abdominal segments, which are somewhat 

 less developed in the fossil than in the recent species, and in the 

 form of its terminal segment, or middle lobe of the tail, the length 

 of which is to its breadth in the fossil as 8 to 6, and in the recent 

 species as 11 to 6. The sides of the carapace are, in the former, 

 somewhat more uniformly covered with minute raised points, 

 which, in both species, render the surface bistinctly scabrous. 



This specimen derives additional interest from its being the 

 only fossil Crustacea which has yet been found in New Holland. 



the attenuated lateral lobes of the tail, and the filiform appendages of all the 

 abdominal segments, evidently unfit them for swimming ; whilst their fossorial 

 habits are amply provided for by the strength and flatness of the two anterior 

 pairs of thoracic limbs, which are admirably adapted for excavating the sand or 

 hardened mud in which they reside. 



* Zool. Miscell. iii. Mai. Brit. 



f Consid. Gener. Crust. Diet, des Sc. Nat. 



