MODIOLA. 



TESTA asquivalvisi, obliqua, iongitiidinalisj ob- 

 loiigo-subcimeiformis, insequiiateralis, latere 

 antieo minimo, obtuso, postico rotuiiclato, clau- 

 so ; margine antico subliiantiilo ; ligamento elon- 



■ ■ gato, subinterno ; imprcssiones muscularcs diia^, 

 postiea majusculaj aiitica minima, terminalis; 

 impressio muscuiarls paliii irregularis, sinu 

 nulio. 



An eqviivalve^ oblique, longitudinal, oblong, ratlier wedge- 

 shaped_, extremely inequilateral shell ; anterior side very 

 small, obtuse; posterior rounded, closed: anterior mar- 

 gin gaping a little for the passage of the byssus, and 

 forming with the base a line oblique to the dorsal line : 

 ligament elongated, partly internal; muscular impressions 

 two, posterior large, irregular, anterior small terminal; 

 muscular impression of the mantle irregular, without 

 any sinus. 



The most important character, which serves to distin- 

 guish Modiola from Mytilus^ consists in the smaller side of 

 the former advancing before the umbones and giving the 

 shell a rounded termination anteriorly. In every other 

 respect it resembles Mytilus, to which it was united iu 

 most of the older books, in connection with other genera 

 that are exceedingly distinct, as we have already shown. 

 The Modiolae, like the Mytili and many other genera affix 

 themselves to submarine productions by means of a bundle 

 of rather coarse fibres^ commonly called a byssus, each 

 fibre of which is fastened to the rock by its expanded 



