38 CIDARIS 



test, and the spine appertaining thereto, is removed by the discovery of the interesting 

 specimen figured in PI. II, fig. 4, a. The spines of this species were first discovered in 

 the Craie chloritee of Essen and Frohnhausen, and were named by Bronn velifer ; as the 

 asperities on their globular stem impart a peculiar character to them, and that author, in 

 his ' Index Palaeontologicus,' referred them to a Salenia. M. Desor described a small 

 Cidaris Heberti from the Craie chloritee of Cap la Heve, which I believe to be the test of 

 this species. The short diagnosis given in the ' Synopsis ' agrees so well with the speci- 

 mens before me that I have no hesitation in concluding it to be the same : — "Petite espece 

 a scrobicules petits et serres, mats a tubercules tres-gros, surtout a la face superieure. 

 Quatre rangees de granules ambulacraires" 



The ambulacral areas are slightly sinuous, and furnished with four rows of small 

 granules (fig. 2, e) closely set together, the marginal rows being the most uniform in their 

 arrangement. The narrow poriferous zones lie in a deep groove formed by the prominence 

 of the adjoining granules ; the pairs of small holes are obliquely inclined, with thickened 

 septa, each having a small tubercle (fig. 2, e) between them. 



The inter-ambulacral areas have two rows of tubercles placed so near the poriferous 

 zones that the inter-tubercular space in the middle of the area is about the same width as 

 the ambulacra, whereby the ten rows of tubercles are situated nearly equidistant from each, 

 thus imparting a regular appearance to this species (fig. 2, c, b). There are five tubercles 

 in each row, which increase gradually in size from the peristome to the disc ; the three 

 basal tubercles are small and set closely together (fig. 2, b), whilst the two upper tubercles 

 are large and wide apart (fig. 2, c); the mammillary eminence is depressed, the areolae are 

 narrow (fig. 2, e), and their margin surrounded by a circle of well-defined granules 

 (fig. 2,/). The tubercle is large and prominent, and the narrow boss on which it rests 

 is destitute of crenulations (fig. 2, e,f) ; the summits of all the tubercles are perforated, those 

 on the upper part of the test are, however, best preserved. A broad band of granula- 

 tions separates the two rows of tubercles ; five or six rows of granules are closely placed 

 together ; and the granules in the band and those in the ambulacra are nearly of the same 

 size. 



In the specimen figured at 4, a, there are seven spines attached to the test in their 

 natural order. The spines (fig. 3, a) have a very short neck and a large globular stem, 

 covered with rows of pointed elevations (fig. 3, b) rising from the midst of an apparently 

 villous surface. The milled ring (fig. 4, b) is close to the acetabulum, it is moderately 

 prominent, and crowded with fine lines. From the manner in which these globular spines 

 are arranged on this small test, very little individual motion was possible among them, 

 and yet the delicate surface of the spines, when examined with a lens, gives no evidence of 

 abrasion, from the friction of moveable bodies laid so closely together as these spines were 

 placed. 



Affinities and differences. — The test of this beautiful little Cidaris is nearly related to 



