BY F. RATTE, ING. DES ARTS ET MANUF., PARIS. 1071 



unrepresented in the other types of Crinoids and all other 

 Echinoderms." .......... 



" Carpenter's reasoning in regard to the basal plates is, that, as 

 the genitals in the Echini, and the basals in most Palseocrinoids, 

 which are generally considered to be their homologues, are situated 

 interradiall y with regard to the general symmetry of the body, we 

 must expect to find the genitals inPalseocrinoids in the same relative 

 position ; and that, in forms like Cyathocrinus, which have two 

 rings of plates below the radials, the lower or proximal plates are 

 situated in line with the radials, and hence cannot be the true 

 basals. He holds that the same order of plates cannot be radial in 

 one genus, and interradial in another. This argument is unques- 

 tionably a very strong one, and we (the authors of the " Revision") 

 are enabled to confirm it by a number of interesting observa- 

 tions." (1) 



Although I feel justified in giving these quotations, on the 

 ground that they lead to a readily useful end in a new and better 

 understanding of fossil crinoids, I cannot follow the authors in 

 illustrating their numerous observations in support of Carpenter's 

 views, and I beg only to record briefly a few simple instances. 



It has been said that the basals must be interradial in position. 

 Then in some genera which have no underbasals, but which have 

 three irregular basals forming a pentagonal figure, namely, 

 Platycrinus (fig. 1), Symbathocrinus and allied forms, it is 

 necessary to show that these basals are interradial in position ; 

 this is done by supposing the two larger plates formed by the 

 conjugation of two smaller piecas respectively ; if, therefore, they 

 are subdivided as shown by dotted lines, it will be understood 

 that the resulting five pieces will be interradial in position. In 

 Belemnocrinus, and in the recent genus Rhizocrinus, the basal 

 pentagon is formed of five pieces, which are, therefore, naturally 

 interradial in position. Ln Eucalyptocrinus and 3feloc? , i?ius ) the 

 base of which is also a pentagon but composed of four plates, one 

 being larger, this larger plate can be divided, and then all the 

 basals become interradial in position. 



(1) Revision, Part I. pp. 239, 240. 

 69 



