TEMNOPLEURID/E. 291 



genera as young Echinidse. However such identifications have usually resulted 

 from superficial or careless examination of the specimens and it is doubtless true 

 that a careful study of any specimen will enable one to determine to which family 

 it properly belongs. 



THE SPINES, PEDICELLARLE, SPH/ERIDIA, AND SPICULES. 

 Plate 93, figs. 16-21, 24-31, 33-36. 



The resemblance of the Temnopleuridse to the Echinidse in all these charac- 

 ters is very marked and characteristic features are not found in any of them. 

 Our researches add little of importance to the detailed accounts already published 

 by Mortensen. The spines sometimes furnish helpful characters for distinguish- 

 ing species though little reliance can be placed on them. In Amblypneustes, 

 for example, Mortensen makes the form of the tip of the spine, whether club- 

 shaped or not, an important specific character. This is not very satisfactory, 

 as it is difficult to decide in the case of some spines whether the tip is club- 

 shaped or not and in some specimens both club-shaped and simply blunt spines 

 occur. In Temnotrema, the smoothness or roughness, and the form of the tip, 

 of the spines is often a useful means of separating species, but even in this genus 

 the lines between the different kinds of spines are sometimes difficult to observe. 



The pedicellarise are so similar to those of the Echinidse, that a description 

 of their characteristic features would be but a repetition of what has already 

 been stated (p. 236-238). The spicules are uncommon and hard to find; they 

 are triradiate in Hypsiechinus, according to Mortensen, but elsewhere are 

 bihamate or simply bow-shaped. The sphseridia show no peculiarities. 



THE GENERA AND SPECIES OF RECENT TEMNOPLEURID.E. 



As first pointed out by Duncan, the Temnopleuridse fall into two groups 

 which may well be ranked as subfamilies. One of these has been designated as 

 Temnopleurinse and this name has been generally agreed to, but for the other 

 group several names have been suggested. Of these the one proposed by Morten- 

 sen but later rejected by him, Trigonocidarinse is preferable. Our choice is due 

 to the fact that it is based on a recent genus and for obvious reasons, it is desir- 

 able that whenever possible names should be based on recent types. No doubt 

 fossil species are of equal importance with the recent in determining the history 

 and natural relationships of Echini; indeed they have often proved of far greatsr 



