MOLLUSCA. 499 



The peduncle Is sliort, and consists of numerous unequal- 

 sized tubular threads, attached by a complicated tendino- 

 rauscular apparatus, chiefly to the larger valve. The spiral 

 arms seemed to have simple summits, and to be destitute 

 of testaceous plates. The smallness and probable youth of 

 the subject, however, rendered a minute examination of the 

 structure impracticable. Trawled up by us in Loch Broom, 

 near the harbour of Stornoway, 16th August 1821. This 

 species approaches nearest to the T, truncata. 



The fossil species of this genus are numerous, and occur 

 in the older and newer floetz formations. They furnish ob- 

 vious characters for the construction of many genera, some 

 of which have been already established. 



2d Subdivision. 



Shell sessile. 



56. Ckiopus. Under valve cemented to stones. 



The under valve is membranaceous, flat, and adhering; 

 the upper is flatly conical, and resembles a Patella, in which 

 genus, from neglecting the structure of the animal, it has 

 usually been placed. 



The C. anumalus. Patella anomala of Muller {Zool. 

 Dan. tab. v. f. 1. 8.), has a branched, double ovarium, with 

 round eggs. It has been described and figured by us as a 

 native of the Zetland seas, under the term Patella distorta 

 {Edin. Enct/clopadia, vol. vii. p. 65. tab. cciv. f. 4. ; and 

 by Montagu, Linn. Trans, vol. xi. p. 195. tab. xiii. f. 5.) 



Order U. — Bivalvia. 



Mouth destitute of fringed spiral arms. 



The animals of this group form the class Conchifera of 

 Lamarck, the Bivalvia of the older naturalists. The 

 shells exhibit great variety of form and relative size. 

 They are joined together at the hinge, which is either plain 



lis 



