188 MYTILID^. 



Gibbsii is said to diifcr in having these shreds serrated or gashed 

 along one edge. I cannot but strongly suspect, though I cannot 

 demonstrate it, that this apparent extension of the epidermis is a 

 parasitic vegetable ; and that M. Gibbsii is not, in reality, a differ- 

 ent shell, but has a dii'ferent vegetable growing upon it. 



Old shells arc also encrusted with various species of Madrepore, 

 CoraUina, and Flustra. 



In young shells there is usually a broad, waxen-yellow radiation 

 from the beak along the front side of the elevated ridge ; and this 

 region, in fact, always has a lighter color than other parts of the shell. 



Deshaycs thinks it is now impossible to say what was the true 

 Mijtilus modiolus of Linnasus, and therefore approves the course of 

 Lamarck in dropping the name altogether and assuming a new one. 

 1 cannot see any reason to doubt that the shell under consideration 

 was the M. modiolus of Linnteus, while there is ground to question 

 whether the shell which Lamarck had in view when he applied the 

 name Papucma, the name now universally applied to our shell, was 

 in reality identical with our species. I have seen several specimens 

 of the East Indian shell, and, though very closely allied, it seems to 

 differ in many particulars when the two shells are placed side by 

 side. Dr. Loven has lately assured me that this is the true M. 

 modiolus, and repeats my conjectures as to the distinctness of the 

 real 31. Papuana. 



The animal is of a dark orange, or red-ochreous color, perhaps a 

 little tinted with brown. It is not used for food with us, though 

 there seems to be no reason why it should not be as palatable as 

 most of the shell-fish that are eaten. 



Modiola plicatula. 



Fig. 81. 



Sliell oblong, falciform, widening posteriorly ; surfixce traversed by numerous 

 radiating ribs, occasionally branching ; epidermis glossy, green and yellow. 



Hfi/tihis di'missw, DiLLwrN, Catal. i. 314. — Wood, Index, pi. 12, fig .'sO. 



Modiola plicatula, Lam. An. sans Vert. vii. 22. — De Kay, N. Y. Moll. 184, pi. 14, fi;,'. 



2.58. — Gould, Tnv. 1st ed. 125, fig. 81. 

 Mijtilus plimtulus, Deshayes, Encyc. Meth. Vers, ill. 5G8, pi. 220, fig. 5. — Soweuby, 



Genera, fig. 7. 

 Modiola semi-costata, Conkad, Journ. Acad. Nat. Sc. vii. 244, j)l. 20, fig. 7. 

 Lister, Conch, pi. 353, fig. 196. 



Shell transversely oldong-ovate, much elongated, narrow before, 

 and widening backwards, somewhat falciform or arched ; beaks 



