8 GEOLOGICAL MEMOIRS. 



O/i Joi7ited Tentacles or Plnnulce, composed of Calc-spar, found 

 on the Ambulacral spaces of the Pentremites. By Dr. Fred. 



ROEMER. 



[Leonhard and Bronn's Jahrbuch, 1848, p. 291.] 



A FORTUNATE discovery in the beds of the carboniferous Umestone on 

 Mount Sano, a hill near the town of Huntsville in Alabama, in North 

 America, has enabled me to add something to our knowledge of the 

 remarkable genus Pentremites, in consequence of which its position 

 in the system must be essentially altered. 



The Pentremites, as is well known, exhibit on the surface of their 

 spherical or pear-shaped shell five distinctly bounded spaces, which 

 diverging like the rays of a star from the central opening above, pass 

 down the sides of the body and are pierced by longitudinal rows of 

 minute holes or pores. These divisions have been compared with the 

 ambulacral spaces of the Echinides ; and in consequence, Say the 

 founder of the genus, Goldfuss and others who have subsequently 

 studied its characters, have considered the Pentremites as a connect- 

 ing link between the Crinoids and the Echinidse. 



Hundreds and thousands of specimens, which I have either col- 

 lected myself in the Western States of the Union or seen in the mu- 

 seums there, all show these spaces penetrated by pores, and without 

 any appendage or covering. In the specimen discovered in the above 

 locality in Alabama the case is different, as I shall now more minutely 

 describe. 



The specimen is a Pentremite about an inch long, belonging to a 

 species intermediate to Pentremites fore alls and P. pyriformis. Say. 

 Only one side of the body is visible ; the remainder is concealed in the 

 rock, — which also contains a fragment of that remarkable coral of the 

 genus Archimedes, Lesueur, which, not less than the Pentremites, is 

 characteristic of the lower division of the carboniferous limestone in 

 the "Western States. The exposed side shows distinctly — two of the 

 three basal or pelvic joints ; — two of Miller's so-called scapulae, stand- 

 ing on the former and bifurcating so as to receive the supposed am- 

 bulacral spaces ; — further, one of the five trapezium-like pieces which 

 stand on the obliquely truncated points of two adjoining scapulae* ; — 

 and lastly, two of the five so-called ambulacral spaces. 



These spaces exhibit the truly singular peculiarity of the specimen. 

 They are covered with highly delicate appendages or tentacles, com- 

 posed of minute fragments of calc-spar, and placed close together in 

 two regular longitudinal rows on each space. 



The structure of these appendages is similar to that of the tentacles 

 or pinnulse (as they are more correctly named by Johannes Miiller 

 in contradistinction to the membranous feelers or tentacles, which also 

 appear there) on the arms of the Crinoids. 



The basis of each of them is formed by a single portion of calc-spar 

 which is obtusely bevelled above ; to this succeeds still smaller thin- 



* These have not been observed by any one except Dr. Troost, who has con- 

 tributed so much to our knowledge of the natural history of the Western States. 

 Compare Transactions of the Geol. Soc. of Pennsylvania, vol. i. p. 224 et seq. 



