14 



The Spondylidae (Thorny Oysters). 



By W. T. Manger, 



{Read April \\th, 1904.) 



The shells which I have selected to say a few words to you about 

 belong to the family Spondylidae (thorny oysters), coming imme- 

 diately after the oysters proper, which, however, they do not resemble 

 either in their internal structure or in outward appearance ; they more 

 closely resemble the Pectens (scallops), but are more spiny and 

 heavier, and united by strong interlocking teeth. They have no 

 byssus, and the ligament is internal, whilst the mantle margin has a 

 row of eyes like the Pectens ; like them, also, they are sometimes 

 brilliantly coloured, and they live, with few exceptions, attached by , 

 one of the valves to rocks, stones, coral or shells. Sp07idylus 

 aurantius is sometimes found attached to Chama lazarus. Chama 

 is totally different to \\-\*t Spondylus, being one of the principal families 

 of the sub-order Cardiacea (to which belong the cockles). From 

 the fact that small quantities of water are sometimes enclosed in 

 cavities in the inner layers of the shell, they have been called wjter- 

 clams or water Spondyli. Woodward tells us that the secretion of 

 colour by the mantle depends greatly on the action of light ; shallow 

 water shells are as a class warmer and brighter coloured than those 

 from deep water, and bivalves which are habitually stationary (like 

 Spondyli/s) have the upper valve richly tinted, whilst the lower one 

 is colourless ; this is not, however, always the case. Spondyhis leuca- 

 cantha is richly coloured on both valves. There are about seventy 

 living species of Spondyhis, and about eighty fossil, and they are 

 met with in depths up to about 100 fathoms of water. They are to 

 be found in all the warmer seas, the Pacific, West Indies, West 

 America, Mediterranean, etc., but it has no representative in Britain. 



Spondyhis, like the oysters, are free swimmers at birth, but in a 

 very short time they settle down and become attached to something, 

 and some species are contorted and twisted in very curious shapes. 

 Pearls are sometimes found in Spondyii, more especially in Spondyhis 

 gcedaropiis, and they are usually of a green or rose colour. As a 

 consequence of the great beauty of most of the species they have 

 always been eagerly sought after by collectors, and years ago, when 

 these things were rare, they have fetched very high prices. 



