new Species of Grinoids. J 59 



cup-shaped, with distinct bilateral symmetry. The surface 

 covered irregularly with minute tubercles, to which were 

 articulated delicate spines, similar to those of an Echinus. 



The base of the calyx is open cup-shaped, consisting of 

 three equal or subequal plates, which, at their margins, form 

 a six-sided figure. There are three series or zones of radials 

 (3x5). The first or true radials (R l ) are large, subequal, 

 flattened, quadrangular plates, and, like a spade, are wider at 

 their summits than at their bases. Their distal margins are 

 either straight or slightly elevated towards the centre, which 

 is considerably thicker than the rest of the plate and has a 

 semicircular excavation, with a finely ridged facet for the 

 reception of the second radial. This so-called second radial 

 (R 2 ), the first brachial (br. 1 ) of Zittel, is a short four-sided 

 joint or plate, which reaches very little above the margin of 

 the first radial, in which it is iuserted. The third radial (R :i ) 

 or axillary, the br. 2 of Zittel, is pentagonal, and either shorter or 

 longer than the second. On each of the facets of its upper sur- 

 face it bears an arm (ay) , so that there are ten arms altogether. 

 The plates or joints of the lower portion of the arms are in 

 a single vertical series, whilst higher the joints are wedge- 

 shaped and disposed alternately in a double series. The 

 pinnules (pi) consist of five or more joints each. A single inter- 

 axillary plate (int) is present between the lower arm-joints. 



A large anal plate (A), nearly resembling in outline the first 

 radials, but narrower at the distal margin, is inserted on the 

 posterior side of the body between the two first radials. Its 

 summit is on a level with that of the radials. The anal inter- 

 radial area, or the space immediately above the anal plate and 

 between the second and third radials and the lower arm-joints 

 on either side, is occupied by three vertical zones of small 

 plates, with six or seven plates in each zone {lb. A) . The anal 

 aperture is not shown in any of the specimens yet discovered. 



In each of the other areas bounded by the distal margins of 

 the first radials below, the second and third radials and the 

 lower arm-joints on either side, and the true plates of the 

 vault above, there are three vertical zones of plates with three, 

 and occasionally four, plates in each zone (lb). The middle 

 plate of the lower zone is clearly larger than the rest. These 

 plates are distinctly interradial in position, and might be 

 termed interradial plates ; but as their lateral margins connect 

 only with the second and third radials (which are merely 

 radials in a conventional sense) and with the lower arm-joints, 

 I prefer to follow Zittel in designating them interbrachial 

 plates. Both these and the anal interradial plates are of the 

 same character as the primary radials and basals of the calyx, 



12* 



