20 P, HERBERT CARPENTER. 



base as a whole is not homologous with the monocyclic base ; 

 for it contains radially situated plates which are absent in the 

 latter. The variations of the apical system in Ophiurids and 

 Asterids throw much light upon this question; for while 

 some forms have one ring of plates within the radial primaries 

 (PL I, figs. 3,4, 6—8, 15), others have two (figs. 1, 2, 12, 14, 16), 

 and others none (figs. 9, 13). But it would be wholly incorrect 

 to say that the plates marked 2 and 3 in Ophiorausium 

 validum (fig. 2) were collectively homologous to the single 

 plates marked 3 in O. flabellum or O. granosum (figs. 

 3, 7). The logical result of this would be that both these sets 

 of plates, together with their respective radial primaries (4), 

 are collectively homologous with the radial primaries of 

 Ophiomusium pulchellum (fig. 9; 4) or the interradial 

 primaries of Ophiomitra exigua (fig. 5; 3); for the latter 

 are the only plates intervening between the radial shields and 

 the dorsocentral. 



It appears to me that the question turns upon the often 

 forgotten difi'erence between homology and analogy. Trauts- 

 chold remarks : *' Basalplatten zu nennen, die sich in der 

 Mitte zvvischen dem unteren und oberen Plattenkreise befinden, 

 wird immer paradox erscheinen, ganz unerklarlich aber dem, 

 der noch nicht in die Feinheiten des Baues der Echinodermen 

 und in die subtilen Deductionen der Forscher eingeweiht ist.^' 

 This is doubtless true, but is it not more confusing to multiply 

 names unnecessarily ? The terra " under-basals " explains 

 itself and is at once indicative of a dicyclic type. 



All writers have agreed that some alteration of the Miillerian 

 terminology is necessary to the scientific study of Crinoids. 

 Probably the least paradoxical change would have been to 

 retain De Koninck^s name, subradials, for the parabasals of 

 dicyclic forms, and also to transfer it to the basals of the 

 monocyclic types. The name " basals " would thus be retained 

 only for those plates which occur in dicyclic Crinoids and are 

 now generally called '^ under-basals." I considered this ques- 

 tion carefully before proposing to use the terms basals and 

 under-basals for the plates of the dicyclic base; but was met 



