ORAL AND APICAL SYSTEMS OY THE ECHINODERMS. 363 



Pentacrinus. Five primary cords proceed from the dorsal 

 angles of its fibrillar envelope, and enter the central canals 

 of the five basals, in which they bifurcate. In the Penta- 

 crinoid larva of Comatula there is precisely the same 

 relation between the primary cords proceeding from the 

 chambered organ, and the five plates (figs, i, v, 3, 3) which 

 are placed interradially upon the uppermost stem segment, 

 the future centrodorsal piece (fig. i, cd), and have hitherto 

 been regarded as true basals. And yet these plates are 

 called parabasals by Loven ! 



Fig. V. — Calyx of the young Aniedon. (After Dr. Carpeuter.) 3, 

 Basals. 4. (First) Radials. Dark Hues as in fig. iv. 



This important morphological fact seems to me conclusively 

 to demonstrate the correctness of Allman's interpretation of 

 the proximal ring of plates in the Pentacrinoid (figs, i, v, 

 3, 3), which, like Loven, I regard as homologous with the 

 genital plates of Echini (fig. ii, 3, 3). They are true 

 basals, interradial in position, and therefore not homologous 

 with the radially placed " first parabasals " of Marsujyites 

 (fig. Ill, 2, 2), as supposed by Loven. Miller^ gave the 

 name " costals " to the last-mentioned plates, and Loven has 

 adopted the name as a general one for the plates forming the 

 proximal ring in the apical system of most Echiuoderms, 

 some Crinoids excepted, i.e. the genitals of Echinus (fig. ii, 

 3, 3), and the basals of Comatula (figs, i, v, 3, 3). It is 

 extremely unfortunate that he has done so, because Miller 

 was not always consistent in his terminology, and employed 

 this one name in his various generic descriptions to designate 

 plates which are now recognised as belonging to at least 

 three distinct systems. (See the table on page o'd>%.) 

 1 Loc. cit., pp. 13G, 137. 



