94 HEMICIDARIS. 



figure where the spines are imperfect."* The figure given by Young and Bird of 

 Hemicidaris intermedia found in the Coralline Oolite of Yorkshire is so bad, that, had I 

 not seen the specimens said to be the type of this figure, and which were undeniable 

 specimens, I should have hesitated before including it in the list of synonyms. The 

 description of the species, however, by Mr. Young,f is very accurate, and is, at the 

 same time, the first given of this species. Dr. Fleming! described it under the name 

 Cidaris intermedia, giving, as its specific character — " Lesser compartments half the width 

 of the larger ones ; tubercles crenulated at the base :" which was rather a generic than a 

 specific diagnosis. 



Hemicidaris intermedia is sub-globose, varying from a depressed spheroid to a conoidal 

 form (PI. Ill, fig. 1 c, i) ; the upper surface is slightly depressed and the base is flat; the 

 ambulacral areas are narrow, and gently undulated towards the upper part ; the semi- 

 tubercles occupy the basal third of the area ; of these there are six pairs, which gradually 

 increase in size from the peristome upwards (PI. Ill, fig. 1 b) ; the two uppermost pairs are 

 rather prominent (fig. 1 d) ; the sides of the areas support two marginal rows of minute, 

 perforated tubercles (fig. 1 d), raised on small elevations — a few microscopic miliary granules 

 separate the rows, and form semi-circlets around the base of the eminences ; the poriferous 

 zones are much undulated, especially in the upper part ; the pores are in pairs throughout 

 the zones as far down as the third pair of semi-tubercles, where they become irregular, and 

 fall into oblique rows, having three pairs in each ; five or six such oblique rows extend to 

 the peristome, and fill up the space left by the smallness of the lower semi-tubercles. There 

 are eleven pairs of pores opposite one of the large plates at the equator. 



The inter-ambulacral areas are more than three times the width of the ambulacral, and 

 furnished with eight pairs of large, prominent, primary tubercles (fig. 1 c) ; the mam- 

 millary bosses form prominent projecting cones (fig. 1 e), the areolas of which touch those 

 of the adjoining ones in the same range ; the areolated spaces of the plates in each row 

 are therefore confluent (fig. 1 d) ; down the middle of the areas, and following the zigzag 

 centro-sutural line, there is a conspicuous double row of small, well-marked, perforated 

 tubercles (fig. 1 d), amongst which some minute miliary granules are scattered ; there are 

 seven of these small tubercles round the centro-sutural edges of each of the larger tubercular 

 plates (fig. Id); a single row of the same sized small tubercles separates the external or 

 zonal border of the areas from the poriferous zones, there being about six small tubercles 

 around the edge of each large plate (fig. Id). By this arrangement the upper and lower 

 boundaries of the areolas surrounding the bosses are confluent, whilst the outer and inner 

 boundaries thereof are surrounded by the small tubercles described (fig. 1 d). The summits 

 of the bosses are deeply sculptured with fourteen well-marked crenulations (fig. 1 d,e) ; the 

 tubercles are large and deeply crenulated (fig. 1 e), and maintain their proportional size on 

 the upper part of the areas (fig. 1 a). 



* 'Medals of Creation,' vol. i, p., 344. f 'British Animals,' p. 4/8. 



X 'A Geological Survey of the Yorkshire Coast,' p. 211. 



