358 J. A. Douglas — New Chalk Crinoids. 



cor-icstudinarium and Micmstcr cor-anguintun. In none of the other zones are the 

 flints of a suitable nature. The actual range of the calyces is, in ascending 

 sequence : — 



4. Zone of Ehynehonella Ciivieri ) ■ ... -n „ „ ,i t i t w^- 1 1 

 „ TT , ^ J t Hi situ. Dover and Isle ot >> iirht. 



3. ,, Holaster planus ... } ' 



2. ,, Micraster cor-testudinaritim. Chatham and Seaford (flint meal). 



1. ,, Micraster cor-anguinum. Chatham, Keston, and Xorthfleet (flint meal). 



1 have no doubt that they have a wider range, but the necessary hollow flints are 



not forthcoming, and it is useless to look for them on soft rock surfaces. 



The reason for their great abundance in the Micraster cor-testudinarmm zone in my 



collection is that at Seaiord Head there is an abundance of the peculiar hollow flints 



which alone yield flint meal." 



Description. 



General Characters. — Calyx minute, funnel-shaped, pentagonal or 

 stellate in oral view. Eadials five, long, with relatively large articular 

 facets, which are bounded on either side by upright projections given 

 off from their inner lateral margins. These projections are grooved 

 externally, and the lateral projection of one radial fuses with that of 

 the next adjoining to form a single interradial spine, which has a slight 

 inclination outwards, and exhibits a median external carina bounded 

 by two grooves. 



The outer, i.e. aboral, face of each radial is provided with a distinct 

 flange. This may be in the form of a rounded keel, the lower end of 

 which is produced downwards and outwards below the base of the 

 calyx, or of a thin wing-like process. In a single instance the. flanges 

 were partially obliterated by regular nodular thickening. 



Situated between the radials may be seen, in lateral view, rounded 

 or oval thickenings, which from their analogous position to well-marked 

 plates in Extracrinua probably represent basals fused into the cup. 



The radial articular facets are horizontal, or with a slight outward 

 slope ; they usually exhibit external fossae and central axial canals. 



Tegmen, arms, and stem unknown, though the articulation for the 

 latter was observed in one form. 



Average dimensions of the common form — - ^ 



Total length of calyx with radial projections • ... -133 inch. 



Length of interradial spines... ... ... ... -013 ,, 



Length of downward prolongation of radial ... -Oi ,, 



Diameter of calyx Avithout projections ... ... "06 ,,' 



Affinities. — This minute criuoid possesses certain characters in 

 common with the Liassic '■ JExtracrinus hriareus,^ namely, radials with 

 an external keel and downward prolongations ; the latter, however, in 

 JExtracrinus are jointed, whilst no trace of this is observable in 9ur 

 form. The keels, on the other hand, are developed to a much greater 

 extent. 



The fusion of the plates renders comparison difficiilt. but the unusual 

 development of the radials above mentioned seems to furnish sufficient 

 grounds for the foundation of a new genus, for which I propose the 

 name Boveacrinus, after Dr. Rowe, their discoverer. 



Two distinct species appear to be well marked, 



Boveacrinus alata, sp. nov. (PI, XVII, Figs. 1, 2.) 



Calyx stellate in oral view, the rays of the star being formed by the 

 thin wing-like processes of the five radials (Fig. 1, r.). The breadth of 



