112 OALYPTIUEID^B. 



beyond the shell, of which it was normally an inside partition. 

 Thus our Calyptneid was fixed as immovably as any Pholas, but 

 with this difference in their condition : that the Pholas, being 

 designed for that kind of life, is not troubled with useless heads 

 and eyes, and, moreover, is furnished with two long pipes to 

 convey the water to and from the mouth and gills ; while the 

 Crucibulum had eyes simply to stare at the wall in the dark, 

 feelers to push the stone, and a long ribbon tongue, armed with 

 hundreds of teeth, to rasp the water. And while encumbered 

 with these unnecessary appendages he had not the benefit of 

 water-pipes, to bring what alone this lock-jawed subject had to 

 feed upon. For this want, however, the economy of the animal 

 provided a remedy. The C. spinosum in its normal growth is 

 either spinose or not ; the flatter forms being almost always 

 smooth. The spires are developed from prolongations of the 

 mantle (or thin shell-bearing skin of the animal), which appear 

 at irregular intervals, though in regular pattern. Sometimes 

 the whole shell is covered with crowded prickles C. hispidum, 

 Brod.), sometimes a few long spines appear at the edge on one 

 side of the otherwise smooth shell. Sometimes the spines are 

 few, large and hollow (C. tubiferum, Less.), each of the outer 

 row communicating through a hole within the inner margin, 

 which is afterwards filled up. Our prisoner worked for his 

 living by constructing very large, long and open spine-pipes, 

 which, instead of standing up at right angles to the shell, were 

 directed back towards the narrow opening in the stone. It 

 would appear that by this means the animal was simply supplied 

 with nourishment, for the shell was above the ordinary size. 



" The most common Calyptraeid on the backs of our Spon- 

 dylus valves, however, was Grepidula aculeata, Gmel. It was 

 first described from West Indian specimens, which are generally 

 dead and worn in collections, and afterwards re-described from 

 fine West Coast shells, as C. hysirix and C. echinus, Brod. 

 The stunted northern form was named C. Californica by 

 Nuttall. 



" Perfect specimens brought by Mr. Dyson from Honduras 

 correspond so exactly with those from Mazatlan that it is hardly 

 possible to resist the impression that they are identical. Speci- 

 mens from South Africa, from Sydney (Australia) and from the 



