112 



chtena and Asper gilium. The mantle is a closed sac, having only an 

 opening for the passage of the siphon and a small slit at the opposite 

 end for the passage of a rudimentary foot : the use of this slit in 

 Clavagella is obviously difFerent from that assigned by M. Riippell 

 to the corresponding structure in Aspergillum. 



Mr. Owen describes the mantle and its structure ; the siphon ; 

 and the thick mass of muscular fibres at the anterior part of the 

 mantle, which forms probably one of the principai Instruments in the 

 work of excavation : he also notices the great development, as com- 

 pared with the size of the animal, of the adductor museles. He 

 then proceeds to the viscera, ■which generally agree with the typical 

 structure in other Bivalves. The digestive system, which accords 

 with that -vvhich is usual in Acephalous Mollusca, is described ; as 

 are also the respiratory and circulating systems, the principai ner- 

 vous ganglia, and the ovary. 



The paper was accompanied by drawings iUustrative of the several 

 structures described in it. 



The specimen described belongs to the species termed by Mr. 

 Broderip Clavagella lata. 



