1844.] 



361 





4'' 



V --" 



Thalassina Emerii Bell. 



a. View of the under side, showing the tail turned over upon the belly. 



b. Side view. 



c. End view, showing the rostrum only. 



tances from the shore. The species of the genus Gehia, which is 

 very neai'ly allied to the present, are all to be obtained by digging 

 in the mud or sand at low tide ; and the Gehia stellata, as stated 

 by Dr. Leach, form subterranean, horizontal, and winding passages, 

 " often of a hundred feet or more in length." The same habit is 

 also known to belong to Callianassa, another nearly allied genus. * 



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

 Thalassina scorpioides, is stated by Leachf, Desmarest|, 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 



* The structure of these animals is adapted only for this mode of life, and is 

 exhibited typically in the present genus. The narrow semicylindrical abdomen, 

 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. 



f Zool. Miscell. iii. Mai. Brit, 



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



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