01" TKE TEST OF THE TEMNOPLEUElDiE. 355 



spherical ; and their free surface is not one of fracture, but is 

 perfect. Some are elongate, and others are elliptical and even 

 very long at their base. The size varies in the species ; and 

 ■jj^^ inch may be taken as a common diameter and height. The 

 sockets are corresponding depressions in the edges of the plates ; 

 and their surface shows an even, unbroken, calcareous reticulation. 

 They receive the knobs ; and no derm passes down, from without 

 inwards, in the line of suture to separate them. The processes on 

 and between which the knobs and sockets are placed in adult 

 forms, are boundaries of the sides of the pits ; and I think that 

 now and then there is continuity between the opposed processes 

 of the two adjoining plates. 



The number ofthekaobs and sockets is immense; and they 

 are found on all the plates, which may amount to more than 

 1500 in a well-developed Salmacis sulcata. The test, as a whole, 

 has no other bonds of union than these sutures ; but the gene- 

 rative and ocular plates are not sutured with the others. "When 

 whole, the tests will stand considerable pressure ; but when 

 partly broken, they fall readily to pieces. The suturing is of a 

 kind which is used in carpentry in making tables, and especially 

 in uniting hollow spheres made up of pieces, when outer and 

 inner bracing is not possible. It is called dowelling. I have 

 not found this method of suturing in other genera ; but irregula- 

 rities of surface on the edges of plates are seen in some. Thus, 

 in Diadema setosum there is a faint trace of an irregular suturing 

 by processes. 



YII. Classiftcatory Conclusions. 



It would appear, from what has been written concerning the 

 sutural depressions and pits, that it is not unreasonable to sepa- 

 rate those Echinoidea with true pits from those which have only 

 sutural grooves or depressions between raised ornamentation, 

 and to consider the grooved forms, which are not pitted, more 

 embryonic than the others. 



The species which were described by MM. D' Archiac and Jules 

 Haime from the Nummulitic rocks of Sind were placed by them 

 under the genus Temnopleurus. But they have no true pits, only 

 well-marked broad grooves over the margins of the sutures ; 

 and these grooves are really parts where the raised ornamentation 

 of the test does not exist. 



LIFN. JOUEN. — ZOOLOGT, VOL. XVI. 25 



