BELL ON A FOSSIL THALASSINA. 



93 



4. On the Thalassina Emefji, a fossil Crustacean, fonvarded by 

 Mr. W. S. Macleay, from New Holland. By T. Bell, F.R.S., 



Professor of Zoology in King's College, London. 



Thalassina Emerii Bdl. 



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



b. Side view. 



c. End view, showing the rostrum only. 



This fossil, forwarded from Mr. Macleay and brought by Lieu- 

 tenant Emery from Australia, belongs to the typical genus of a 

 very remarkable family of decapod Crustacea, the Thalassinidce 

 ( Thalassiniens of Milne Edwards), as Mr. W. S. Macleay has sur- 

 mised. Of the genus in question, Thalassina, but a single recent 

 species is known, and little has been ascertained respecting its 

 habits. There is, however, reason to believe, that in this respect 

 it agrees with the species most nearly allied to it in structure, 

 several of which being found on our own coasts have afforded 

 opportunities for more accurate observation. These, as far as 

 their habits have hitherto been traced, are all of them burrowers, 

 making their way to a considerable depth in the sand at various dis- 

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

 very nearly allied to the present, are all to be obtained by digging 

 in the mud or sand at low tide ; and the Gebia 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 structure of these animals is adapted only for this mode of life, and is 

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



