434 Herbert L. Hawkins — Studies on the Echinoidea. 



least of a functional kind, and definitely stated that jaws could not 

 have existed in the genus. He ridiculed (with some justice) the 

 figure of the teeth given by Forbes, ascribing them to grooves made 

 in the infilling chalk of the specimen by the use of a graving tool. 

 As a result of his denial of the existence of jaw-structures, he 

 detached Conulus from its hitherto unassailed position among the 

 Holectypoida(Echinoconidae) and relegated it to the group containing 

 Pyrina and Echinoneus. 



That Duncan was wrong in denying the presence of a perignathic 

 girdle in Conulus is patent to all who care to develop the interior of 

 the adoral surface of any species of the genus ; it is difficult to 

 understand how so reliable an observer could have overlooked such 

 an obvious structure, and have succeeded iu blinding the perception 

 of another worker of the standing of W. P. Sladen. Thus his chief 

 argument against the occurrence of jaws in the genus is based upon 

 inaccurate observation, and, indeed, recoils. Since there is a peri- 

 gnathic girdle, and the main purpose of such a development is for the 

 attachment of the muscles that work the jaws, the presence of the 

 latter structures must logically be inferred until disproved — a difficult 

 or impossible proposition. The two sole bases for such a negative 

 argument are, firstly, the non-discovery of the ossicles in question, 

 and secondly, the obliquely elliptical outline of the peristome. 



The transfer of Contdus to the Echinoneidae by Duncan may or 

 may not be justified, but an entirely different complexion was put 

 upon such a change by the discovery by A. Agassiz in 1909, of 

 a fully developed lantern in a post-larval Echinoneus. Although 

 this vestigial lantern is resorbed before the mouth becomes functional, 

 its complete development at such a relativel)' late stage in ontogeny 

 is a clear indication that the recent Echinoneidae have descended 

 from ancestors which were gnathostomatous at no very remote 

 period. The post-larval lantern of Echinoneus is associated with 

 a simple, but defined, perignathic girdle. This girdle is com- 

 pletely resorbed at the same stage of ontogeny as the lantern. 

 On the inevitable hypothesis that Echinoneus and Conulus are nearly, 

 if not directly, related, it would be expected that the latter genus 

 should show a longer persistence of the jaw-apparatus, but that, as 

 its ontogeny progressed, the structures should steadily degenerate. 

 The last anticipation, so far from being justified by the known facts, 

 is directly negatived by them. The largest specimen of Conulus 

 albogalerus in which I have studied the perignathic girdle shows that 

 structure developed into far greater complexity and perfection of 

 detail than it presents in smaller examples. Hence it is reasonable 

 to argue that, since the loss of the lantern in Echinoneus coincides in 

 time with the complete destruction of the perignathic girdle, the 

 retention and specialization of the girdle in gerontic specimens of 

 Conulus indicates that the lantern was persistent throughout life. 



In 1911 I was able to describe and figure actual teeth, with 

 characters and proportions little different from those of Discoides, in 

 a specimen of C. subrohmdus. The specimen is fully adult, but it is 

 strangely anomalous to find such relatively small elements as the 

 teeth when there is no trace of the usuallv far more massive 



