246 CATALOGUE OF THE BLASTOIDEA. 



periphery almost equatorial. Basal plates completely hidden in the columnar 

 cavity, and constituting about two thirds of it, in the form of an inverted deep 

 pentagono-conical cup. Radial plates elongate, extending almost the entire height 

 of the calyx, and slightly turned in below to assist in forming the columnar cavity ; 

 limbs ellipsoidal, very long, obliquely truncated above, with the central line of each 

 limb rather concave ; interradial sutures deep, sinuses sublinear, narrow, with pro- 

 minent edges; radial lips prominent, and their apices projecting. Deltoid plates 

 small, thickened, triangular, with broad bases, and almost horizontally placed, often 

 produced upwards into small, tapering tubes. Ambulacra parallel-sided, projecting 

 slightly above the edges of the sinuses ; lancet-plate subhexagonal in section, its 

 median groove exposed till near the distal end ; side plates very small and numerous 1 , 

 lying on the lancet-plate at a high angle. Hydrospires two on each side of an ambu- 

 lacrum, their sacs large and pyriform; spiracles round, vertically perforating the 

 tube-like projections of the deltoid plates, occasionally double, but the anal spiracle 

 oval, and more nearly on a level with the summit of the calyx, protected on the outer 

 side by a large node or tubercle. Mouth small. Column of round thin joints. 

 Surface of the radial plates bears oblique, rounded, and minutely granular ridges, 

 and intervening impressed lines, directed from the edges of the sinuses laterally 

 towards the interradial sutures, the longer ones converging to the narrow portions of 

 the plates between the radial lips, where they are much crowded together. 



Remarks. This is a very remarkable species, and will well repay close and attentive 

 study. The deep columnar cavity is a very striking and characteristic feature. It 

 is deeper in this Blastoid than in any other with which we are acquainted, even 

 Elceacrimis Verneuili (PI. II. fig. 45). A still more noticeable character in many 

 individuals is the extension of all the spiracles, except the anal one, into erect 

 tubular openings, a feature which was first described by Dr. C. A. White 2 . We 

 figure a very beautiful example of these tube-like prolongations (PI. VII. fig. 5), and 

 are not acquainted with exactly similar structures in any other Blastoid. From an 

 examination of numerous specimens, however, it appears to us that this one must be 

 looked upon as presenting an extreme condition, for in the majority of cases the 

 tubes do not project anything like so far (compare PL II. figs. 32-35). The indi- 

 vidual figured on PL VII. figs. 5, 6, also shows the "solid projection" described by 

 Dr. White as bordering the outer side of the anus. Several of our English species 

 of Granatocrinus have nodes or mammillary projections not only over the anal but 

 also over the other four spiracles (PL IX. figs. 5, 8, 14, 15). We have not, however, 

 noticed any erect tube-like extensions like those of G. Norivoodi. The number of 

 side plates is difficult to estimate ; but according to Owen and Shumard there are 

 two hundred plates on each side of an ambulacrum — one hundred side, and one 



1 Owen and Shumard say one hundred. 



2 Bo«ton Journ. Nat. Hist. 1803, vol. vii. no. 4, p. 483. 



