1886.] NATURAL SCIENCES OP PHILADELPHIA. ST 



ALLAGECRINUS Ether. & Carp. 



1881. Ann. and ]\rag. Nat. Hist. (April), pp. 281-298. 



1884. De Loriol, Paleont. Francaise (Serie i), Tome xi, p. 46. 



Allagecrinus was made by Etheridge and Carpenter the type 

 of a distinct family, and this was accepted by De Loriol. In 

 our opinion it is either a Haploerinoid or no Palaeocrinoid at all. 

 If the five ventral plates, as E. and C. assert, are orals, which in 

 the younger specimens extended to the radials, closing in the 

 tentacular vestibule, but in their subsequent stages were "rela- 

 tively carried inwards, away from the radials, and separated 

 from them by perisome," we should regard Allagecrinus a 

 Neocrinoid. If, however, it is a Palaeocrinoid, we think the five 

 ventral plates are interradials, which in the young Crinoid were 

 closed, and gradually opened out so as to expose the summit 

 plates. In this case, Allagecrinus was in its earlier life morpho- 

 logically in a similar condition as Haplocrinus^ but may have 

 attained in the adult a somewhat higher degree of development. 



Messrs. Etheridge and Carpenter state on p. 284 of their paper 

 on Allagecrinus^ that the mouth in the larger specimens could 

 not have been " roofed over or closed by a dome or vault of any 

 kind," for " if such a structure had existed within the circle of 

 radial plates, it would assuredly have been preserved." To this 

 we reply, that the summit structure of Symbathocrinus which is 

 comparatively solid was discovered after hundreds of the most 

 perfect specimens had been examined, and until then it was 

 regarded as membranous ; the same was the case in Cyathocrinus. 

 Allagecrinus in its more advanced stages, may have attained the 

 conditions of Haplocrinus or Symbathocrinus, or even of Cyatho- 

 crinus^ and passed perhaps through all those phases successively; 

 but there is not the least evidence that the Scheitelplatten in any 

 Palfeocrinoid were carried inward by perisome as in the Neo- 

 crinoidea. 



The same writers remark on p. 286, that " in none of the 

 smaller specimens is there Siny trace of an anal opening, either 

 directly piercing an oral plate, or at the margin of the dome 

 between the orals and radials." And they state further, that 

 " the central end of one or more of the former may be marked 

 by tubercles, but we cannot suggest any explanation of these." 

 If E. and C. had regarded these tubercles as mere ornamentations, 

 they certainly would have stated so. We judge from their figs. 



