48 DE. p. H. CABPENTEE ON CEETAIN POINTS 



with the following remark : — " The difference of the terminal 

 syllable has in many cases been regarded as a sufficient distinc- 

 tion, and is perhaps preferable to adopting a new name. Should 

 it be objected to, however, I propose the name Megacystites.'" 

 This name, minus the terminal syllable, was adopted by the 

 editors of Angelin's ' Iconographia,' who gave its synonymy in 

 1878 and described a new species from Sweden *. Miller quotes 

 this work, but seems to be altogether unacquainted with the 

 change proposed by Hall. For Ifegacystis does not appear in 

 his ' North- American G-eology and Palseontology,' nor in his 

 recent contribution to the Seventeenth Indiana E-eport. 



Another change seems also to be inevitable. JEcJiinodiscus is 

 one of the oldest generic names among the Sea-urchins, having 

 been founded by Breyn in 1732. Descriptions of the genus and 

 of three of its species appear on pp. 531-534 of the ' Eevision 

 of the Echinoidea' by Alexander Agassiz. In spite of this, 

 however, and of Scudder's ' Nomenclator Zoologicus,' Messrs. 

 Worthen and Miller bestowed the name Echinodiscus in 1883 on 

 what they believed to be a new genus of Cystids allied to Agela- 

 crinusf. They state that "the mouth or ovarian pyramid is 

 sub central, w^hile in Agelacrinus it is submarginal. This elevation 

 would seem to be homologous with the mouth in the Echinoids, 

 for below it, within the visceral cavity, there occur several pieces 

 which were evidently connected with the digestive functions, and 

 therefore homologous with the jaws in the latter order." Six 

 years later Miller described this same opening in Agelacrinus as 

 the ovarian or anal aperture J, while he spoke of that of JEcJiino- 

 discus simply as the " mouth ;" and in his latest publication § he 

 describes a new species, E. Sampsoni, in which " the mouth is 

 distant more than half an inch from the central point of the union 

 of the ambulacra." Nothing could better illustrate his extra- 

 ordinary confusion upon this subject and his persistent disregard 

 of the simplest facts in Echinoderm morphology. 



It has been pointed out above that Megacgstis is one of the 

 genera w^hich has a third opening situated behind the mouth in 

 the same interradius as the osculum. Miller continues to call 



* Oi). cit. p. 29. 



t ' Geological Survey of Illinois,' vol. vii. 1883, p. 335. 

 X ' North- American Geology and Paleontology,' p, 222. 

 § ' Seventeenth Eeport of the Geological Survey of the State of Indiana,' 

 Paleontology, p. 70. 



