462 MR. HERBERT L. HAWKINS OX 



blnntness of Clypeastroid teeth. The peculiar structures in 

 C. alhogalerus, usually known as the " buccal plates," are probably 

 in some way derived from jaw-ossicles, as their anomalous 

 character separates them absolutely from the peristomial plates 

 which exist in many other genera. In the paper to which 

 reference has just been made, I have suggested a possible origin 

 and function for the buccal plates, but it must be confessed that 

 the theory advanced there ha,s a very insecure foundation. 



So far as is at present known, there is nothing in the structure 

 of the lantern of the Holectypoida which even foreshadows the 

 curiously expanded pyramids of the Clypeasti'oida. The probable 

 delicacy of texture of the pyramids in Conulus subroiimdus may 

 indicate the incoming of a reticulate structure similar to that 

 of the corresponding parts in Clypeaster. With regard to the 

 manner of working, the angle of setting of the jaws shows a 

 progressive tendency towards the Clypeastroid method. This 

 retention of the " Regular " facies of jaw-structure throughout 

 the grovip is rendered the more remarkable by a comparison 

 with the fi'agmentary pyramids in Conoclypeus described by 

 de Loriol (35). That genus, with its Clypeastroid (almost 

 Echinanthine) general build, seems to have possessed the compact 

 pyramids of a Discoidea. It is true that the only record of its 

 jaws is very imperfect, but this much seems obvious on a study 

 of de Loriol's drawings. But in Conoclyfe%is, in spite of the 

 Holectypoid jaw-structure, the perignathic girdle is very like 

 that of Clypeaster. 



The recently described teeth and lantern in a young sjDecimen 

 of an Echinoneus (Agassiz, 58) have a most important bearing on 

 the relation between the Holectypoida, and the Echinoneidse. 

 The presence of the jaws is undoubtedly a vestigial character, 

 for they seem to be resorbed while the individual is still quite 

 immature. The jaws and teeth both have a Discoidea-Mke 

 appearance, rather than a Clypeaster-isicies. It is probable that, 

 as they exist in the young stages of Echinoneus (the most 

 advanced member of its family), they will have been present in 

 such genera as Pyrina at a corresponding stage of development. 

 The likelihood of their discovery in fossil forms is extremely 

 remote, owing to their minute size and delicate texture, but 

 analogy tells strongly in favour of their existence. This dis- 

 covery is a remarkable instance of the completion by Ontogeny 

 of an unfinished chain of evidence supplied by Palfeontology, 

 and removes any doubt which may have existed as to the 

 intimate relationship which links the Conulidee with the early 

 Echinoneidse. 



In this connection it seems well to suggest the possibility that 

 Loven's genus Pygastrides (Loven, 43), a '■'■ Pygaster" lingering so 

 long after the day of the Holectypoida was past, may be only 

 another example of the vestigial gnathostomatous stage of some, 

 probably Echinoneid, genus. So strongly am I of this opinion, 

 that I have omitted its name from the new classification. 



