On the Scattered Skeletal Remains of Holothuroidea. 191 



The smallest number noticed in an entire plate was nine. 

 The interspaces between the perforations forming the mesh 

 vary a good deal in breadth ; some are comparatively narrow, 

 in others the divisions are broader. 



Of these plates there are certainly two well-marked varie- 

 ties in the size of the perforating holes, and perhaps a third. 

 Beyond mere size, no difference can be indicated between the 

 three kinds, except that, perhaps, in the intermediate variety 

 the perforations are less rounded than in the first, or that 

 possessing the largest holes. The measurements of the two 

 varieties may be taken as follow : 



1. Size of Plate averaging about -V inch= "02 in., longest diameter. 

 Size of perforations about ^^ incli=*005 in. 



2. Size of Plate averaging about ^V incli= '0255 in., longest diameter. 

 Size of perforations about -^^-^ incli= '0045 in. 



h. Hooks or " Anchors" — Accompanying the foregoing plates 

 are simple, generally plain hooks. The shaft has a length of 

 about "0232 inches, and is terminated at the proximal end by 

 an eye, formed by the shaft being bent back upon itself. The 

 distal end is recurved and forms the hook, terminating in an 

 attenuated point. The shaft is quite plain and simple in all 

 the examples examined, but in one specimen the fluke or 

 hook was observed to be dentate, or slightly serrated, on the 

 concave side. These anchors are always single and never 

 doubly fluked. In appearance they are white, glistening, 

 and semi-transparent. 



In two instances the hooks have been observed attached to 

 the first variety of perforated plate, in such a manner as to 

 clearly prove their relation one to the other (PL V., Figs. 5 

 and 6). There is, however, no trace of any process or exten- 

 sion of the plates to which the hooks could have been attached. 

 No doubt this was effected by means of the eye at the proximal 

 end of the shaft in each hook. As compared with the per- 

 forated plates the hooks are rare. 



c. Wheel-like Plates. — Very minute circular, concavo-con- 

 vex, wheel-like plates are met with intermingled with those 

 first described. On the convex face the surface is gently 

 rounded from the margin to the centre, wdiich forms an inner 

 ring, and is either subdivided or entirely hollowed out, ac- 



