300 CARDIASTER 



Dimensions. — Antero-posterior diameter two inches and one tenth ; transverse diameter 

 two inches ; lieight one inch and one tenth. 



Description. — In notes to a hst of British Cardiasters appended to a description of 

 pi. ix, decade iv, of the ' Memoirs of the Geological Survey of the United Kingdom,' 

 Professor Edward Forbes says, "in the Museum of Practical Geology there'is a Cardiaster 

 from the Greensand of Blackdown, remarkable for the small tubercles in proportion to 

 its size and the great width of the hinder lateral poriferous avenues. It seems to be 

 identical with the Holaster hisulcatiis^ described and figured by M. Albin Gras in his 

 ' Oursins fossiles de I'lsere.' " I had a very careful drawing of this rare Urchin made 

 from the type specimen, and placed it (fig. 2 a, h, c) on the same plate with C. fossarius, 

 to show its near affinity with that form. 



The test is cordate, about as long as it is wide ; the anterior border is elevated 

 (fig. 2 b) and deeply indented (fig. 2 a) by the anteal sulcus, which is well defined by the 

 angular folds bounding the depression on both sides (fig. 2 c) ; the central portion of 

 the ambulacrum is smooth and the pairs of pores minute and distinct from each other. 

 The antero-lateral ambulacral pairs (fig. 2 a) are short, narrowly lanceolate, and the 

 postero-lateral pair wider behind ; the poriferous zones of all the avenues are narrow, and 

 their pores are small slit-like apertures. The ambulacral summit is near the anterior 

 border of the junction of the anterior with the middle third of the test. The apical 

 disc which occupies this point is small, compact, and formed of four perforated ovarial 

 and five minute ocular plates. The surface of the plates carry very small tubercles in 

 proportion to the size of the test, a well-marked character originally pointed out by 

 Forbes. A few^ larger tubercles occupy the angles of the sulcus and anterior border, but 

 on the other portions of the upper surface they are very uniformly diminutive. The 

 posterior border much accuminated above (fig. 2 a) and obliquely truncated inwards 

 below (fig. 2 b) ; the anal area is very limited, and the oval periprocte opens at the top 

 of the oblique truncature of the posterior border. 



Affinities and differences. — Cardiaster Perezii resembles C. fossarius in many of its 

 essential characters ; it difi'ers, however, in some minor points in the anatomy of its test ; 

 the posterior half is much more accuminated, the anal area nuich smaller, the upper 

 surface is likewise more inclined from the vertex of the border than in C. fossarius. The 

 tubercles are smaller on the upper surface, but larger, and more developed at the base. 

 The continental authorities as MM. d'Orbigny, Cotteau, and De Loriol, consider this 

 Urchin as a true Holaster. In deference to the opinion of my lamented colleague 

 Professor Edward Forbes I have left it in the genus in which he placed it. 



Locality and StratigrajjMcal Position. — This Urchin is very rare in England, and has 

 been collected only from the Upper Greensand at Blackdown with Ec/nnos^jataffus Murcki- 

 sonianiis. In France it is found in the Gault at Ravis (Isere), and at Clar near Escragnolle. 

 In Switzerland, Perte-du-Rh6ne, Sainte-Croix (Vaud), Wannealp, Oberalp (Wsggithal), 

 Cheville, Bossetan (Valais), and in France, near Nice. 



