224 jMr. F. A. Batliev on British Fossil Crinoids : 



tliis in the earlier part of the paper (p. 209), that it is only 

 necessary to poiiit out that a Sikirian species is here described, 

 from specimens of mature growth, in which the axial canal 

 is not separated from the ventral groove in the radial facet : 

 in this point C. vallatus resembles Carboniferous species of 

 Cyathocrinvs. Further evidence, if such be needed, to show 

 that the non-separation of the canal is merely a youthful 

 character, and tlierefore also an archaic one, may be adduced 

 from tlie young specimen at Jermyn Street (p. 211, fig. 5 a). 

 Consequently it is not in itself a character very suitable for 

 the discrimination of genera. 



The Covering-plates of the Arms. — It does not appear from 

 the present paper, but it will be seen from the descriptions of 

 the Gotland Cyathocrini that, altiiough the number of these 

 that goes to an ossicle is variable, yet there are limits to the 

 variation, by the recognition of which we are often able to 

 determine species when other means fail us. 



In describing these structures, JMessrs. Wachsmuth and 

 Springer have mentioned (Rev. I. 84, Proc. 1879, p. 307) that 

 the groove " is provided with two rows of from two to five 

 successive movable plates, alternately arranged on opposite 

 sides." It is, however, undoubtedly the case, as shown by 

 PI. XIII. fig. 10, that the row on either side may be only 

 one plate deep. It is quite true that there are sometimes 

 two plates in the row, a small narrow plate lying at the base 

 of and alternating with each of the regular conical covering- 

 plates (see Angelin, Iconogr. tab. xxvi. fig. oh). Occa- 

 sionally too there occur small, usually rather irregular plates, 

 over the middle line, between the two rows of regular 

 covering- plates. This might make three or conceivably four 

 rows on either side (see W. & S. Rev. III. Proc. 1885, pi. iv. 

 fig. Ih). But in asserting that there were sometimes five 

 rows it is possible that Messrs. Wachsmuth and Springer 

 were misled by Angelin's tab. xxvi. fig. 4, which represents 

 the covering-plates of C. ramosus (wrongly called there G. 

 longimamis) ; for these plates are marked by transverse lines 

 that divide them into five parts, and produce the impression 

 that each covering-plate is composed of five ossicles, which is 

 not really the case. 



The Ventral Sac. — Messrs. Wachsmuth and Springer stated 

 in 1879 (Rev, I. 84) that pores and slits had been observed 

 in the ventral sac of Silurian species of Cyathocrinus. This 

 statement has never been withdrawn by them, though in their 

 recent paper on the Perisomic Plates* they seem to imply 



* Troc. Acad. Nat. Sci. Philadelpbia (1800), Tart III. See p. 360, 

 rebniarv 1801. 



