18 P. HERBERT CARPENTER. 



however, he is using the word parabasals in a new sense. But 

 it is obviously the one which he intended ; for he speaks of 

 the parabasals (basals mi hi) as passing over to the ventral side 

 and becoming mouth-shields. Apparently, therefore, he does 

 not find any homologues in the Ophiurids for the orals of 

 Crinoids; and yet the relation of these plates to the vascular 

 systems is the same as that of the mouth-shields in Ophiurids 

 as was pointed out by Ludwig. His comparison of the dorso- 

 central of Ophiopyrgus with that of a stemless Crinoid 

 shows that he considers the dorsal regions homologous in 

 Crinoids and Ophiurids; but at the same time he compares 

 plates which are ventral in the Ophiurids with others which 

 are dorsal in the Crinoids. This seems to be on account of 

 the so called " dorsal origin " of the mouth-shields, a point 

 which I believe to be more apparent than real. They can only 

 be called dorsal if they are developed around the right vaso- 

 peritoneal tube, which is as yet not proved ; and I more than 

 doubt if it ever will be. 



Studer follows Zittel in retaining the name "parabasals" for 

 the upper row of plates beneath the radials of dicyclic Crinoids. 

 The latter author^ fully accepts the homology between them 

 and the " basals " of the monocyclic forms ; but he thinks that 

 the change of terminology necessitated by calling them basals 

 would lead to confusion, owing to this name having been 

 previously applied to the lower ring of plates on which the 

 parabasals rest. There is, indeed, a certain advantage in the 

 retention of the name parabasals, as it indicates at once that 

 the type under consideration is one with a dicyclic base. But 

 this indication is already given in the expression under-basals ; 

 and the use of two names for one and the same set of plates 

 seems to me calculated to mislead future workers, who will not 

 be, as we are now, in a transitional period between empirical 

 and rational methods of nomenclature. The bones of the 

 carpus and tarsus, or those of the skull are not renamed for 

 every variation in number and arrangement which they 

 present. Certain elements are constant and others variable. 

 ' 'Handbuch der Palaeontologie,' i Band, pp. 327, 338. 



