224 THALASSINADiE. 



and a little rounded forwards ; the outer lamina rather 

 longer than broad, the whole ciliated at the margin. 



Length, about an inch and a half. 



The discovery of this species, according to Leach, is due 

 to Mr. Gibbs, who found it in the King's-Bridge Estuary. 

 Montagu says that it was taken with Callianassa suhterra- 

 nea^ in a sand-bank at that place ; and he supposes it 

 to inhabit the burrows formed by the Solenes. It is, how- 

 ever, not to be doubted that it forms its own burrows ; 

 and Leach states that " it has been taken on some of the 

 shores of Plymouth Sound, under the mud of which it 

 makes long winding horizontal passages, often of a hundred 

 feet or more in length."'"' 



The burro Aving of these fossorial species is a subject 

 which deserves more attention than has hitherto been paid 

 to it. The means by which it is effected are at present 

 absolutely unknown ; nor is it yet certain whether they 

 ever avail themselves of the labours of other animals, or 

 whether the excavations in which they are found are 

 wholly the work of their own hands. The account given 

 above, from Dr. Leach, of the extent of these passages, 

 appear at first scarcely credible, and may well challenge 

 a thorough examination of these points in the economy of 

 these curious animals. 



The difference of the depth which the various species of 

 this fossorial family inhabit is very remarkable ; the pre- 

 sent species, with Callianassa suhterrama, being found in 

 a sand-bank, when digging for Solenes,'''' whilst Calocalis 

 Macandrew was dredged from the astonishing depth of 

 one hundred and eighty fathoms. 



