] 26 POTEEIOCEINID.E PENTACRmUS. 



9 Species. Pentacrinus basaltiformis. (Milhr.) 

 Plate 10, Figure 1 a, to 1 e. 



A description of the neat column of this species is all that can be given at present, 

 for although thousands of specimens of this portion of the animal have been found, no 

 part of the body has yet been met with. No additional information has therefore been 

 obtained since Miller first noticed its occurrence in the Lias, a fact which was previously 

 known to Parkinson. 



The column is composed of numerous ossiculas, which are nearly of equal size and 

 thickness throughout its whole length, always excepting the newly formed and immature 

 joints, which are, according to the universal law as regards the growth of this part of 

 crinoids, invariably introduced at, or near the summit. The articulating facets of the 

 joints vary according to their distance from the body. In those occupying positions 

 near the summit, the spaces between the oval, or floriform crenated ridges are wider 

 than on those more remote from it. In other words, as the joints became by age more 

 indurated and possessed increased powers of adhesion, the petal like markings gradually 

 expanded until they obliterated the intervening space and occupied the whole attaching 

 surface of the joints, and thus we frequently find them in a fossil state. 



The column appears to have been of nearly uniform diameter from its base to its 

 articulation with the body. Each joint is ornamented with minute tubercles which are 

 symmetrically arranged, but varying in arrangement on their joints according to their 

 remoteness from, or proximity to the body. These tubercles are sometimes arranged 

 quadrangularly, at others they appear in the form of a double waved line, while, not 

 unfrequently each group has a cruciform appearance. From this, and similar variations. 

 Miller deduced his theory respecting the gradual deposition of the calcareous substance 

 of the column, a conclusion which cannot well be doubted, although • his ingenious 

 attempt to illustrate his views by the presence or absence of tubercles may be fairly 

 questioned. 



Round auxiliary claspers occur at intervals along the column, in series of five each. 



Synonymes and references. 

 Pentacrinite — Park. Org. Rem. vol 2, PL l^,fig. 54, 



Pentacrinite basaltiformis. — Mill. Nnt. Hist. Crin.p. 62. 

 — Morris, Ott Brit. Foss. p. 55. 

 — Goldf. PI. 52, Jig. 2 a. to 2g, p. 172. 



