334 Mr. A. Hancock on Shells dredged on 



but is I think distinct ; it is about the same size and has the like 

 strong, transverse ribs ; the rostrated end, however, is not so long, 

 is less arcuated, is more abruptly truncated, and the umboncs are 

 nearer the centre. Breadth T 9 ¥ inch ; length T 5 ¥ inch. 

 Two specimens were dredged. 



Modiola nigra, Gray. 

 Modiola nigra, Gray, App. Parry's 1st Voy. p. 244. 

 Mytilus discrepans, Mont. Brit. Shells, Supp. p. 65. t. 26. f. 4 

 (not of the body of the work). 



A fine series of specimens were brought, some of which are 

 totally black, others are varied with olive-brown ; and the young 

 are of a pale greenish olive : the striae are considerably coarser 

 in some than in others, and the dorsal margin is occasionally 

 more arched than usual. Some of the largest are -If inch long 

 and J inch broad. 



Modiola laevigata, Gray. 

 Modiola Icevigata, Gray, App. Parry's 1st Voy. p. 244. 

 Mytilus discors, O. Fabr. Fauna Grcenl. p. 418? 



An extensive suite of this fine Modiola was procured ; many of 

 them are much larger than those from which Mr. Gray described ; 

 some are If- inch long and 1-i- inch broad. 



There is, however, no doubt that they belong to this species : the 

 surface being almost devoid of radiating striae gives to it a very 

 characteristic appearance. 



Dr. Gould, in his ' Report on the Invertebrata of Massachu- 

 setts/ includes this species amongst the synonyms of his Modiola 

 discrepans, which is quite distinct from the shell so named by 

 British conchologists*. 



The Modiola discrepans of Gould is probably the M. laevigata, 

 but there are several points of difference. The latter is less 

 winged on the dorsal margin, and is more abruptly rounded at 

 the posterior end ; the radiating ribs on the anterior portion are 

 not straight as in that species, but are regularly waved and are 

 more numerous, there being sometimes as many as fifteen ; but 

 even on this portion of the shell, the ribs are generally more or 

 less obliterated, and consequently it is difficult to ascertain their 

 number. The posterior compartment is almost always smooth, 

 but occasionally traces of very fine radiating striae may be ob- 

 served at the margin. The middle compartment has rarely a few 

 distant, fine, depressed radiating lines ; the whole surface is a 

 good deal wrinkled concentrically, and the epidermis is very 



* The Modiola discors of Gould appears to be the true M. discrepans of 

 Montagu (not of the Supplement), differing only by having a few ribs more, 

 on the anterior compartment : and the M. nexa of the same author is the 

 M. nigra — the discrepans of Montagu's Supplement. 



