from the Lias and Oolites. 381 



five mammillary eminences disposed around the union of the 

 column with the calyx. 



The rays are short and robust ; the primary portion consists 

 of two pieces, a flat basal plate and a triangular brachial plate ; 

 the basal plate has a slight elevation on its outer and upper 

 articular surface; the brachial plate has the form of an equi- 

 lateral triangle, it is very convex externally, and has its base firmly 

 planted on the flat basal plate, and its sides support the se- 

 condary rays ; these are ten in number, and consist of from ten to 

 eleven circular plates, each diff'ering in form and thickness from 

 the other, their articular surfaces being smooth and undulated 

 in different directions, the elevations of the one plate always 

 corresponding to the depressions of the other with which it is 

 articulated ; these inequalities are well seen in the specimen 

 before us ; from the various angles at which these plates lie in 

 relation to each other, the ultimate brachial piece of each of the 

 secondary rays has a triangular form externally, the sides of 

 which support the tertiary rays ; these, like the secondary rays, 

 consist of unequal-sized plates with undulated articular surfaces, 

 which are marked with fine lines that radiate from the centre to 

 the circumference ; the number of the elements in these ter- 

 tiary rays cannot be accurately made out in consequence of the 

 imperfection of this part of the skeleton ; judging however from 

 the remains of the plates in a part of the slab once occupied by 

 a tertiary ray, we estimate their number to have been from fifteen 

 to twenty. The inferior surface of the centre of the calyx ex- 

 hibits a depression produced by the convexity of the brachial ele- 

 ments and the prominence of the heart-shaped basal pieces; into 

 this depression the summit of the column closely fits. It is 

 unfortunate that so small a portion of the column of this 

 Crinoid is preserved, as it is possible that the lower part of the 

 stem was diff'erent from that which is preserved; the upper part 

 of the column before us consists of thin star-shaped plates, the 

 rays of which are deeply divided, and their surfaces are sculptured 

 with well-marked transverse articular processes; between every 

 third plate a thicker and broader plate is introduced ; the side- 

 arms appear to have been numerous about the upper part of the 

 column ; they were composed of thin circular plates having un- 

 dulated surfaces similar to those observed on the secondary and 

 tertiary rays. 



Affinities and differences. — Pentacrinm Goldfussii resembles in 

 some points P, tuber culatuSy Mill. : through the kindness of 

 Major Austin and Mr.Etheridge w^e had the privilege of comparing 

 our fossil with Miller's type specimen in the Bristol Museum, but 

 the imperfection of that Crinoid makes a rigorous comparison 

 impossible ; one point of difference which Miller thought specific 



