524 VERRUCID.E. 



sary, as well as in the case of the fixed terguni, owing to 

 the altered shape of the summits of the moveable scutum 

 and tergum, due to their corrosion and to their coming to 

 project freely. But the most remarkable character of the 

 fixed scutum is, that on the under side there is no great 

 adductor plate, but a rounded hollow with its lower edge 

 only slightly prominent ; the absence of the adductor plate, 

 which is present in all the other species of the genus, is 

 no doubt due to the under side of this valve being inclined 

 even outwards, and so standing in some degree opposed to the 

 moveable valve ; thus affording on its under surface a place 

 for the attachment of the lower end of the adductor scu- 

 torum muscle ; whereas in the other species this muscle 

 could not possibly have been attached, without the aid of 

 an adductor plate, to the under side of the much depressed 

 and sloping fixed valve. The fixed tergum (t') is a little 

 more simple in form than the corresponding valve in the 

 other species ; the two arms, answering to the occludent 

 and carinal margins of the moveable tergum, are more nearly 

 equal in length : the internal transverse ledge, separating 

 these rims or margins from the parietal portion of the valve, 

 is but little developed. 



All four valves forming the shell are remarkable from 

 having, when full-grown, but not whilst young, their basal 

 edges abruptly inflected inwards, thus forming a ledge all 

 round the basal membrane, as in Chthamalus intertextus and 

 Hembeli. 



Moveable Scutum. — This is slightly larger in proportion 

 to the tergum than in the foregoing species : it is chiefly 

 remarkable from the presence of three prominent longi- 

 tudinal ridges on the main part of the valve, like the two 

 articular ridges on the tergal margin ; of these latter, 

 the lower one extends down to about the middle of the 

 tergal margin. The moveable tergum is rhomboidal, with 

 the whole carinal portion marked only by lines of growth : 

 it is only remarkable by the upper of the three articular 

 ridges on the scutal margin being unusually distinct from 

 the occludent margin. 



With respect to the animal's body, its several peculiari- 

 ties have already been pointed out under the genus. The 



