H. L. Hawkins — Morphology of Ecltinoidea. 449 



In passing, it is of great interest to find that Conulus, the deep- 

 water member of the group, is in so many respects the most 

 "Holectypoid". The so-called "Cretaceous" fauna of the deeper 

 parts of the Atlantic Ocean has often been regarded as owing its 

 " antediluvian" character to the similarity of conditions in the ooze- 

 belt of deposition, at whatever period it exists. This explanation, 

 and the companion one that the reduction in the struggle for 

 existence in thinly populated depths encourages the persistence of 

 types whose extinction is overdue, seem reasonable enough, but they 

 can hardly account for the revival of Holectypoid qualities in Conulus. 

 Excepting Discoidea, Conulus is the only genus of the Holectypoida, 

 as far as can be ascertained, that was not absolutely littoral in 

 habitat. Its reassumption of Holectypoid features cannot, then, 

 have been due to a return to "Holectypoid" surroundings ; nor is 

 there any reason to regard it as moribund. Perhaps, since the trend 

 of normal Holectypoid evolution was one of improving adaptation to 

 shore-line existence, Conulus, in abandoning that sphere of life, 

 allowed the specially adaptive features to lapse and degenerate, 

 while spurring on others for accommodation to the new and 

 unfamiliar surroundings. In some such way it is possible to 

 reconcile the combination in Conulus of some features more Holecty- 

 poid than those of its presumed ancestor, Pyrina, and of others far 

 less Holectypoid than those of its sister JSchinoneus. 



The relationship between the three genera suggested in the 

 preceding sentence appears to me to be the only one possible. It 

 can hardly be said to be proved, but it accords with all known 

 qualities of the forms concerned. The detailed analysis of some 

 tubercle-patterns in certain species of Conulus that follows adds 

 further points of support to the hypothesis. Thetaxonomic corollary 

 which would follow its acceptance is clear. If Conulus is an 

 Holectypoid (it would be unfortunate to exclude it from an order 

 that was once called " les Galerites"), and if Conulus was derived 

 through Pyrina, how much the more must Pyrinahe an Holectypoid? 

 Echinoneus must surely be placed in the same order with Pyrina. 

 The only serious difficulty in the way of such a systematic grouping 

 (assuming the phyletic foundation to be sound) comes in the 

 uncertainty as to the ancestry of Pyrina. That genus may well have 

 arisen from some such Pygasteridse as Macropygus or Anorihopygus, 

 but it is unlikely to have included any of the JLolectypus series in its 

 ancestry. The tubercle-pattern of Anorthopygus is distinctly Pyrinid, 

 and its peristome is far from circular. But various Jurassic genera, 

 among which forms called Desorella, Nucleopygus, or Pyrina are 

 most noteworthy, might perhaps be claimed as forerunners of the 

 Cretaceous group. If such a claim were substantiated, Anorthopygus 

 would be too late to fall into the phyletic line. However, it would 

 seem that the Jurassic forms that resemble Pyrina in shape and some 

 other characters are always covered by tubercles whose order of 

 inception is indeterminable. It would be very strange to find 

 Irregular Echinoids, that had advanced so far beyond Holectypoid 

 limits in this direction, reverting to the " Regular " quality of 

 sparse, coarse, and serial tuberculation. In default of definite 



DECADE VI. — VOL. VI. — NO. X. 29 



