206 ORGANIC REMAINS. 



the pleuroci/sti, which have it in the side, or on the upper surface. Some 

 species of all the three classes occur in our district, being found in the 

 chalk, the oolite, the calcareous sandstone, and in nodules of flint in 

 the alluvium ; and a few specimens of them are given in Plate VI. 



The first class (anocysti) comprises two divisions; the cidaris, or 

 tnrban, and the clypeus, or hucMer. No. 1, PI. VI, is a beautiful 

 cidaris from the Malton oolite, corresponding with that figured in 

 Parkinson's Organic Remains, III, PI. I. Fig. 6, and considered as a 

 variety of cidai-is pajnllata. It is marked with five double rows of 

 large mammilla, or tubercles, disposed alternately ; each of which is 

 surmounted by a small papilla, having a minute hole or puncture in 

 its centre, and a crenulated ring surrounding it. Around the base of 

 each tubercle, except where it conies in contact with that of the next 

 in the same row, is an elegant circle of minute mammillee, shaped 

 exactly like the large mammillae which they inclose, each having its 

 punctured papilla in the centre. The portions of these circles in the 

 interior of each double row come nearly together, and form two lines 

 of minute warts, curiously waved, with a bending suture between the 

 lines. Immediately beyond the exterior portions of the same circles, 

 in the space or area left between the double rows of large tubercles, 

 we find on each side a double row of minute pores, each having 

 usually an elevated margin ; Avhich rows run in a bending line, fol- 

 lowing the curvature of these portions of circles. Each of the five 

 spaces contains two of these double lines of pores, between which is 

 left a small space, adorned with two rows of small mammillae, placed 

 alternately. Towards the vertex whei-e this space is very narrow, 

 these mammillae are minute ; but near the base they become larger. 

 Between these two rows runs another ilexuous suture, like that in 

 the interior of the main rows ; and as cross sutures, passing between 

 every two of the large tubercles, join these longitudinal sutures, the 

 whole shell is thus divided into compartments or plates. Some very 



