20 THE VOYAGE OF H.M.S. CHALLENGEE. 



ends at the sixth node. This is due to the great length of the internodes in this species 

 (PI. XVIII. fig. 3 ; PI. XIX. fig. 1). 



Pentacrinus maclearanus presents exactly the opposite type of structure. There are 

 only twelve nodes in the stem of the solitary individual obtained (PL XVI.). But these 

 all occur in a stem barely 40 mm. long, as there are never more than two, and generally 

 only one internodal joint ; while the cirri cluster thickly round the stem, so that it has 

 an appearance more like that of Exti-acrinus hriareus than is commonly met with in the 

 Pentacrinidse. It is noteworthy that in the last-named sjjecies the stem does not seem 

 to have reached any great length, and that it sometimes tapered downwards.^ 



This peculiarity was also noticed by MM. Eudes-Deslongchamps in some stems 

 belonging to a large colony of Pentacrinites which they discovered in the Great Oolite 

 of Soliers, near Caen ; ' while it is very characteristic of Millericrinus lyratti from the 

 same horizon in Gloucestershire ; ' and also of the Carboniferous Woodocrinus, certain 

 Blastoids, and of the Silurian Glyptocystites, Pleurocystites, and other forms. The most 

 remarkable instance of this in a fossil Crinoid, however, is that of the Lower Silurian 

 Gly2)tocrinus schqfferi of S. A. Miller/ for which he has recently established the new 

 genus Fycnocrinus. In one specimen found by Miller the lower jiart of the stem was 

 " wound around a Crinoid column of a distinct species, almost as neat as a thread can be 

 wound upon a spooL The column gradually tapers as it coils, until it becomes so smaU 

 as to be scarcely visible to the naked eye, the larger plates of the column which, give it 

 that banded appearance, or make it resemble a string of small spools, gradually diminish, 

 and before the column terminates it becomes as smooth as a silken thread." 



Two other species from the same locality at Cincinnati, Lichenocrinus dubius and 

 Dendrocrinus navigiolum, were also found by Miller to have tapering stems. In the 

 case of the former he infers that " the column was free and used to direct and guide 

 the course of the animal through the water, and perform such other functions as were 

 performed by the columns of other floating Crinoids, except that it was never used 

 for purposes of attachment." One must not, however, conclude at once, from the 

 tapering condition of the stem in a fossil Crinoid, that the animal was free in its habits. 

 In a young Eucalyptocrinus crassus, for example, which is figured by HaU,' the stem 

 tapers downwards very considerably, but is attached below liy a spreading root. 



I have found a tapering stem in certain individuals belonging to six species of 

 recent Pentacrinidge, but it appears to ha the exception rather than the rule, and is 

 therefore entirely devoid of any systematic value. 



1 Encriniden, p. 271. 



- Etudes sur les I'tages Jurassiques i:ifi-rieurs de la Normandie, Paris, 1864, p. 232. 



■' On some new or little kno^ra Jurassic Crinoids, Quart. Jov/m. Geol. Soc, vol. xxxviii. pp. 31-33, pi. i. figs. 6-8, 

 10-14. 



* Description of i'oiir new Species and a new variety of Silurian Fossils, and remarks upon others, Journ. Ciiicinn. 

 Soc. Nat. Hint., vol. iii., 1880, pi. vii. fig. 3, p. 2 (of separate copy). 



5 Tweuty-eiglitli Annual Report of tlie New York State Museum of Natural History, Albany, 1879, pi. xvii. fig. 5. 



