SEA-URCHINS. 491 



madreporic genital extending liglit through the system to occupy 

 some part of the posterior border.' In every case the liftli 

 genital is absent, and this feature alone serves to distinguish 

 a 8patangid from the great majoi'ity of the " Cassidulidaj." At 

 lii'st sight there do not seem to be many points of resemblance 

 l)et\veen Anorthopygus and the Spatangidie. However, the 

 stratigraphical appearance of the two types is the same, and, 

 in the structure of the apical system, Anorthoi>ygus shows an 

 ethmolysian character in both the known species. No types of 

 Echinoids other than Anorthopygus and some Spatangids have 

 this feature. The position of the periproct in the Holectypoid 

 genus is about midway between the apex and the ambitus, and 

 the same character holds in almost all the Spatangidje. In 

 several small specimens of A. orbicularis that 1 have steii there 

 is an appreciable increase in the declivity of the test behind the 

 periproct, and I regard this as a rudimentary posterior surface, 

 Tlie plating of the periproct-membrane also shows some similarity 

 in the two groups. 



The evidence for their genetic affinity is very slight, but I have 

 ventured to connect the Spatangida; with the Anorthopygus line 

 of descent on account of the apical structure and stratigraphical 

 correspondence. 



4. Conulus and A mhl yj}y gus. 



Amhlypygns is a Tertiary Echinolampid (Duncan (44) classed it 

 as an Echinoneid) whose characters are best known from the 

 descriptions of Indian species given by Duncan and tSladen (39). 

 The shape of the test, the obliquity of the peristome, and more 

 especially the structure of the ambulacra, all show features of 

 similarity with those of the Conulidse. The ambulacra are sub- 

 petaloid adapically in Amhlypygvs (a mai-ked contrast to all the 

 Echinoneida?), but in that region, as much as on the adoral 

 surface, the inclusion of one demiplate between two primai-ies 

 is i-egularly shown. It is difficult to imagine that this peculiar 

 structure could be evolved independently in heterogenetic 

 genera. The only other form with which Amhlypygns could 

 be associated by reason of tins structure is Uisc/wlectypus, but, 

 apart from the contrasts which the two genera sliow in other 

 respects, the stratigraphical sequence is not favourable. As 

 Amhlypygus is a veiy primitive type, and one of the oldest 

 known genera, of the Ecliinolampidse, I have separated that 

 family from the other " Cassidulida?," and derived it from the 

 Conulid stock. The later members of the family seem to have 

 reduced their ambulacral structure to a condition of simple 

 primaries ; a process that, outside the order of the Holectypoida 

 seems to have been the usual one adopted. 



5. Conulus and C onulojysis. 

 A group of Upper Cretaceous Echinoids, which was formerly 

 classed with " Galerites" was separated from that genus bv 



