HEXACRINUS. 199 



Austin's specimen hardly seems to show all the particulars in regard to the 

 arms which he describes, and it is only smooth because its surface is destroyed. 

 Its anal parts have unfortunately been scraped away, but one of Mr. Vicary's 

 specimens shows them better. The anal plate is seen to be headed by a short 

 projecting tube which is channelled within, but the division of its plates is 

 obliterated, and, the specimen being fractured at the top, it is impossible to tell 

 what length it reached. The first columnal is seen in this specimen. 



Affinities. — The three forms, H. microglyphicus, Vicarii, and quintangulus, are 

 evidently closely related, and from the poverty of our meterial it is exceedingly 

 hard to decide how far the observable differences are specific ; at the same time 

 each form does seem to have a facies of its own, which makes it likely that 

 the distinctions would be more definite if the specimens were better. 



The present form bears some resemblance to H. pater sef or mis, Schultze, 1 but 

 its calyx is deeper and much more definitely hexagonal. 



8. Hexacrintts ? aberrans, Whidbome. Plate XXIII, fig. 3, and Plate XXV, 



figs. 2—2 c. 



1SS9. Platyceinus abereans, Whidbome. Geol. Mag., dec. 3, vol. vi, p. 79. 



Description. — Dorsal cup small, elongate, conical, with slightly convex sides. 

 Attachment of column large, triangularly petalliform, with smooth lower surface 

 except a row of small short crenulations close to the margin. Basal circlet cup- 

 shaped, deep, about one-third the height of the cup, with an irregularly polygonal 

 upper margin, and a constriction forming a small rounded narrow rim at the inferior 

 margin; consisting of three subequal plates, rather broader than high. Radials 

 five, very large, elongate, subhexagonal, with straight rather expanding sides, and 

 with a large deep, semi-elliptic notch extending over the whole upper margin. 

 First primibrachs very small, linear, only partially filling the notch. Second 

 primibrach wide, very short, axillary, triangular at the centre. Anal plates 

 two in the first row, resting on two of the basals, one being narrow, very 

 elongate, hexagonal, and very much smaller than the radials ; the other being of 

 the same size as the radials, but irregular in shape, and produced above into a 

 slight neck or tube, which perhaps is composed of other plates. Structure of plates 

 very thick. Suture-lines rather deep, with a small bevelled border. Surface 

 bearing numerous small obscure pustules. 



Size. — Height 45 mm., width 35 mm. 



1 1S67, Schulzte, ' Denksch. k. Acad. Wissen. Wien,' vol. xxvi, p. 199, pi. x, figs. 4— 4 c. 



