PENTREMITID^E. 211 



rows of plates, and the extreme length and tenuity of its arms. From the mode 

 of their occurrence, however, the specimens may possibly be the immature state 

 of some other form known or unknown. It has been very difficult to distinguish 

 between the upper and lower faces of the arms, which probably very closely 

 resemble each other in general appearance. 



Among British Palaeozoic starfish this species seems most nearly to resemble 

 Protaster leptosoma, Salter, 1 both on its upper and under surfaces, but in that 

 species the central pentagon is smaller and the shape still slighter. Comparing 

 these two species with Furcaster palaeozoicus, Stiirtz, 2 it seems probable that they 

 may be members of the same group. Moreover, Mesozoic species referred by 

 Wright 3 to Ophiurella seem sufficiently similar to make it possible they may be 

 congeneric, while a Devonian species 0. primigenia is referred to Ophiurella by 

 Stiirtz. 4 Again, the figures of Ophiura rhenana, Stiirtz, 5 show details which might 

 correspond with the indications seen in our less well-preserved fossil. On the 

 whole it may be well to leave it temporarily in the genus Ophiurella, to which, 

 even if not actually belonging, it probably is nearly allied. It certainly has 

 nothing to do with Protaster. 



4. CLASS BLAST01DBA, Say, 1825. 

 1. ORDER REGULARES, Etheridge and Carpenter, 1886. 



I. Family PENTREMITID^, d'Orbigny, 1852. 



The species described below appears to fall within this family (as amended by 

 Etheridge and Carpenter) from (1) possessing, as far as can be judged, minute 

 irregularly rhombic deltoids, which occupy the extreme summits of the inter- 

 radial sinuses, and (2) the spiracles being apparently situated in the oral space 

 beyond the deltoids and not within their margins, the ambulacra being rather 

 broad, and hydrospire-slits not being exposed outside them. 



With regard to its generic position, it may be noted that its ambulacra are 

 very long and are broader than the intervening sinuses. Its shape too, as far as 

 can be seen, is more or less a prolate spheroid; but in none of our specimens 



1 1857, Salter, 'Ann. Mag. Nat. Hist.,' ser. 2, vol. xx, p. 331, pi. ix, fig. 5. 



2 1886, Stiirtz, ' Palseontographica,' vol. xxxii, pi. viii, p. 79, figs. 45 a ; and 1890, ibid., vol. xxxvi, 

 p. 2L4, pi. xxxi, figs. 40, 40 a. 



3 1866, Wright, ' Brit. Foss. Echinod. Oolitic Form.,' vol. ii, p. 154, pi. xviii, figs. 3 a, d ; and 



p. 154, woodcut 40. 



4 1886, Stiirtz, ' Palontographica,' vol. xxxii, p. 77, pi. viii, figs. 1 2 a. 



5 1893, Stiirtz, ' Verb. n. h. Vereins Preuss. Bheinl.,' vol. 1, p. 7, pi. i, figs- 1 3 - 



E E 



