1885.] NATURAL SCIENCES OF PHILADELPHIA. 331 



10 X 12 primary arms." This formula was considered by Angelin 

 and Zittel so distinct from that of any other known form, that 

 both placed the genus in an independent famity. We should fol- 

 low their example, if we were satisfied as to the correctness of 

 that description. 



From the fact that Angelin gave the number of most of the 

 above plates with doubt — he stated positively only the number of 

 " parabasalia " — we infer that his specimens in the basal regions 

 were not in a condition for critical examination. It is, moreover, 

 apparent that an arrangement of plates, such as he described, is 

 theoretically, as well as practically, impossible. 



From the description it is difficult to ascertain which of the 

 plates were intended as " basals" and which as " parabasals." In 

 fig. 2, PL 9, of the Iconographia, there are represented close to 

 the column two rings of plates ; an upper or outer one, which is 

 composed of 25 or 26 pieces, and close to the column an inner one, 

 which, if an}- reliance can be placed in the figure (?), contains 

 very nearly the same number, for the plates are represented as 

 alternating with those of the upper ring. The former should 

 contain the "parabasals," the latter the basals; but unfortunately 

 the plates of both rings differ in number most conspicuously from 

 the number attributed to " basals " and " parabasals " in the de- 

 scription. 



Of all the plates to which the description alludes, the " ten (?) 

 bifurcating radials" are most readily recognized, and we believe 

 there are actually ten of these plates in the specimen. In the 

 figure they occupy a position within the second ring, but along 

 with other plates which are interposed between them. At the 

 one side there is a small single piece, which we take to be an inter- 

 axillar}' plate; at the other are found two larger plates, evidently 

 interradials, with possibly an additional anal piece at the poste- 

 rior side. It is very probable that these 15 or 16 plates, which 

 in groups of one, two, and three (?) are inserted laterally between 

 the axillary radials, were taken in the description for " parabasa- 

 lia," as otherwise those plates would be undescribed. If this is 

 the case, the term has been incorrectly applied, as the name 

 "parabasalia " has been given only to the ring of plates which lies 

 beneath the radials, and between these and the underbasals. All 

 plates which are laterally inserted between the radials, as in this 

 case, are called interradials. It would be, however, equally incon- 



