H. L. Hawkins — Morphology of Echinoidea. 447 



It appears, then, that Conulus is rightly regarded as an Holectypoid, 

 although its tuberculation brings it dangerously near the border-Hue : 

 while Pyrina and Echinoneus differ from the normal character of the 

 order merely in shape (a purely relative and very variable quality, as 

 " Globator" shows) and in the absence of any marked triserial 

 arrangement of the orad pore-pairs. The latter feature can be 

 fairly regarded as the successful completion of the tendency towards 

 podial simplification that is persistent in the order. If it is admitted 

 that the resemblances between the three genera are so many that they 

 must surely be closely related in phylogeny, the two insignificant 

 items in the construction of Pyrina and Echinoneus cannot be 

 permitted to exclude them from the Holectypoida. 



That Echinoneus is practically a lineal descendant from Pyrina 

 seems evident. The Pyrina group ranges through the Cretaceous, 

 and species of Echinoneus are restricted to the Tertiary. Save for the 

 position of the periproct and the perforation of the tubercles, there is 

 little difference between the two that could warrant their distinction 

 even as genera. Periproct position points to Conulus as a transitional 

 stage from one to the other, but no other morphological features 

 support that indication. It is true that Conulus occurs chiefly in the 

 Upper Cretaceous, and is definitely of later origin than Pyrina, but 

 its peculiar characteristics make it impossible to believe that Pyrina— 

 Conulus— Echinoneus represents a genetic series. To suggest that 

 Conulus— Pyrina- Echinoneus is the true sequence seems more plausible, 

 since Coyiulus is an accredited Holectypoid, while Pyrina and 

 Echinoneus are much alike and usually considered to be Spatangoids. 

 But there are insuperable difficulties in the way of acceptance of such 

 a hypothetical line of evolution. In the first place, it violates the 

 known stratigraphical order of appearance of the forms, and although 

 such risks may reasonably be taken when ancient and relatively 

 unfossiliferous systems are concerned, it is unjustifiable to call in the 

 "imperfection of the palseontological record" in the case of thick 

 tested marine forms from the Lower Cretaceous. Secondly, Conulus 

 shows specialization of the orad parts of the ambulacra, and 

 complication of interradial ornament, that are definitely in advance of 

 the normal conditions in the Holectypoida, and certainly far more 

 elaborate than the corresponding features in Pyrina and Echinoneus. 

 It would seem in the last degree improbable that such specialization 

 should be evolved merely to sink back to, and even beyond, the level 

 from which it rose. What, then, can be the relation between Conulus 

 and the Pyrina- Echinoneus series ? 



At this stage it is profitable to consider the problem from a different 

 point of view. Echinoneus, the only one of the three genera whose 

 habits can be directly observed, lives (according to H. L. Clark) at or 

 about low-tide mark in sheltered lagoons, clinging feebly to the 

 under surfaces of rocks and picking up small pebbles and other 

 fragments as a protective covering. It is eminently a shallow-water 

 form. There is every reason to believe that the habits of Pyrina were 

 essentially the same. I know of no record of the occurrence of the 

 genus in this country at an horizon higher than the Chloritic Marl — 

 the last well-defined littoral deposit in the English Cretaceous 



