238 



from its being exactly confined to the internal surface, I conceive that it 

 belongs to the original structure of the shell. 



On clearing the larger valve, a reddish hue became very evident, and 

 appeared to be the remains of the original colour of the shell. 



When the straight hinge and box-like form of this, shell is considered, 

 some resemblance will appear between it and the fossils which we have 

 just been examining. But a more material coincidence is discoverable 

 in the strong resemblance which exists between the surface of the back 

 of the larger valve and that of the larger valve of the preceding fossil, 

 Plate XVI. Fig. 17, both surfaces being remarkably smooth, and formed 

 by extremely fine transverse striae. 



CLIV. Hyal&a. A regular, inequivalved, transparent bivalve shell, 

 gaping beneath the beak, tricuspidated at the base. 



This shell was originally described by Forskal, and named by him 

 Anomia tridentata, and as such admitted by Gmelin. Lamarck has very 

 properly placed it in a .distinct genus. It is not known in a fossil state. 



CLV. Orbicula. A very small orbicular, flat bivalve. The lower 

 valve very thin, and adherent to other bodies. The hinge unknown. 



This shell, only described by Muller, and named by him Patella ano- 

 mola, is not known as a fossil. 



CLVI. Lingula. A long flat shell, composed of two valves, nearly 

 equal, truncated anteriorly ; the hinge without teeth : the base or beak 

 of the valves pointed, and united to a tendinous tube, serving for a liga- 

 ment of attachment. 



Linnaeus, who had seen but one valve of this shell, named it Patella 

 unguis. Bruguiere ascertained the nature of the shell, and assigned to it 

 this genus. It has not been yet noticed as a fossil. 



In consequence of the similarity of the animals which inhabit the shells 

 forming the two following genera, Linnaeus disposed them under one 

 genus, which he named Lepas. But Bruguiere and Lamarck have, with 



