CRENELLA. 133 



logy/ published in 1827, being the same year as that in 

 which Mr. Berkeley's notice appeared in the f Zoological 

 Journal/ a circumstance that undoubtedly must have 

 some weight with a scientific jury ; but after consider- 

 ing the whole case, and taking into account the positive 

 disadvantage which would result from a change of any 

 name that has been generally recognized, I must give 

 my verdict in favour of Mr. Berkeley. This species is 

 the Modiola asperula of Searles Wood's Catalogue of 

 Crag fossils. 



2. C. decussa'ta*, Montagu. 



Mytilus decussaftis, Mont. Test. Brit. Suppl. p. 69. C. decussahis, F. & H. 

 ii. p. 210, pi. xlv. f. 2. 



Body greyish-white : mantle quite open in front, and folded 

 at the posterior or broader end of the shell to form an excre- 

 tory tube ; edges fringed with very short and minute glistening 

 cilia, which correspond with the ribs of the shell : tube very 

 short and sessile, with a plain margin : foot worm-shaped, con- 

 sisting of a long stalk with a sheath at the end, from which 

 proceeds an oval creeping- disk. 



Shell obliquely oval, with a slight approach to a rhomboidal 

 form when viewed sideways, rather solid, somewhat glossy and 

 prismatic : sculpture, 50-60 fine longitudinal ribs, crossed by 

 40-50 transverse striae ; the former resemble those of the last 

 species ; the latter are thread-like and form minute nodules or 

 beads on the ribs at the points of intersection : colour pearl- 

 white : epidermis rather thick and yellowish-brown : margins 

 rounded on all sides except at the back, where an obtuse 

 angle separates the hinge-line : beaks globular and prominent, 

 placed close to the anterior margin, over which they slightly 

 project; they are quite smooth, with the exception of some 

 delicate transverse striae : ligament thick, reddish-brown : 

 hinge-line nearly straight : hinge-plate rather broad, finely cre- 

 nulated : hinge toothed as in the last species : inside nacreous, 

 showing more or less distinctly the impression of the ribs ; 

 inner margin notched all round : scars more perceptible than 



* Divided crosswise. 



