224 



MOLLUSCA FROM THE CRAG. 



Length, 1 inch. 



Locality. Cor. Crag, Sutton. Recent, Channel Islands, Hebrides, and Bergen. 



This delicate and elegant shell is rare in my cabinet ; about half a dozen small 

 specimens and a few fragments are all that I have seen. It much resembles the 

 young of Ps. vespertina, but is rather more rounded on the posterior side, and it is a 

 deeper or more tumid shell. The hinge teeth are small, though apparently a trifle 

 larger than those of the recent shell. The palleal sinus is large and deep, extending 

 inwards to a little beyond the hinge denticles. It is said to extend in the living state 

 from the Channel Islands to the coast of Bergen, and ranges vertically from five to fifty 

 fathoms. 



TELLINA,* Linnaeus, 1767. 



PETASUNCULUS. Rumph. 1705. Petiver, 1713. 



CHAMELEA (sp.) Klein. 1753. 



PERONCEA ET PERONEODERMA (sp.) Poll. 1791. 



TELLINARIUS (sp.) Dum. 1806. 



AN GULTJS. Mefferle, 1811. 



OMALA. Schum. 1817. 



ARCOPAGIA. Leach MS. 1816. Brown, 1827. 

 PHYLLODA. Schum. 1817. 

 TELLINIDES. Lamk. 1818. 

 MACOMA. Leach, 1819. 

 LIMICOLA. Id. 1819. Fide Gray. 

 HOMALA. (sp.) Agassiz. 



Generic Character. Shell transversely ovate, or suborbicular, generally inequilateral, 

 plain or smooth, but more frequently sculptured or ornamented ; posterior side more 

 or less angulated, with an irregular flexuosity produced by a slightly sinuated form in 

 the posterior part of the ventral margin. Hinge with generally two cardinal and two 

 lateral teeth in each valve, the latter, in some species, are obsolete. Palleal impression 

 deeply sinuated. Ligament external. 



Animal of the form of the shell, having the mantle open in front, with the margins 

 fringed ; siphons long, sometimes four or five times the length of the shell, separate 

 throughout, the orifices plain or indistinctly toothed ; foot large, triangular, and 

 compressed. 



The character by which this genus is said to be most distinguished is the flexuous 

 fold, or slightly twisted form of the posterior side of the shell ; this, however, is not 

 always discernible, thereby merging into Sanguinolaria and Psammobia which are 

 characterised by the absence of the fold, and the want of lateral teeth, though in some 

 species of this genus the latter character is by no means permanent. The outward 

 form of Tellina is exceedingly variable, some species being nearly orbicular, while 

 others are much elongated ; in general the shells are slightly compressed, somewhat 

 unequal in size, one valve being more tumid than the other, especially on the posterior 

 side, where the ligament is placed ; and this side is generally, though not always, the 

 shorter of the two. 



* Etvm. TeXXtV?;, the name of a mussel. 



