176 CATALOGUE OF THE MOLLUSCA 
When viewed in a living state there appear to be two siphons 
at the longer end of the shell, but only the posterior of these has 
the walls complete ; the other has its anterior side open, formed 
by a fold in the cloak as in the siphons of the zoophagous 
gasteropods. The animal has consequently only two pallial 
apertures. 
4. M. marmarata, Forbes. 
Mytilus descors, Mont. Test. Brit. 167. 
Imbedded in the skin of Ascidia tuberosa and A. sordida, (espe- 
cially the former) from deepish water, common. 
86. CRENELLA, Brown. 
1. ©. piscussata, Jfont. 
Mytilus decussatus, Mont. Test. Brit. Supp. 69. 
Crenella elliptica, Brown’s Ilust. Rec. Conch. 75, t. 23, f. 12-14. 
In shell-sand at Tynemouth, and the Fern Islands, rare. A 
specimen was got by Mr. King in a cavity of a small stone from 
deep water, brought in by the fishermen. Dredged alive in 
seventeen fathoms off Whitburn, by Mr. R. Howse. 
This genus undoubtedly comes very near to the costated division 
of the last ; the crenulated hinge plate, and the deep-seated inter- 
nal ligament appear to be the chief distinguishing characteristics. 
Famity.- Unionipa, Fleming. 
87. ANODON, Cuvier. 
1. A. anatinus, Linn. 
Anodon cygneus, var. 8, anatinus, Gray, Turt. Man. 292. 
In ponds, frequent. 
Captain Brown figures a specimen from Prestwick Car, which 
is about six inches in breadth. It has not occurred to us of so 
large a size. 
88. UNIO, Retzius. 
1. U. prctorum, Linn. 
Unio pictorum, Gray, Turt. Man. 295, t. 2, f. 11. 
Mr. Hoge states that this has been found in the ponds at Wyn- 
yard, on the authority of Sir W. C. Trevelyan, Bart. It has not 
been met with further north. 
