200 GEOLOGY. 



the anus they become much smaller, and run much closer 

 together. The rows of arnbulacral pores are not flexuous above, 

 but close to the mouth they become zigzagged and slightly 

 irregular. The interambulacral plates are broader than high. 

 The number of tubercles, -which varies from eight to nine, or 

 even ten, including a very small one close to the mouth (being 

 rarely seven in very small specimens), is greater than in most 

 allied forms. The spines, many of which occur with the shells, 

 are long, with the remains of longitudinal striation visible upon 

 them : the shoulder near the base is rather wide and granulated, 

 the base also granulated, the intermediate portion shaped like 

 tlie frustum of a cone. The granulation of the shoulder is very 

 slight, and easily disappears with weathering, so that many 

 spines appear as if not granulated here: the granulation cor- 

 responds to the terminations of the longitudinal striae. The 

 apical disc is ill-preserved or wanting in all the specimens 

 found. 



The nearest approach to this form appears to me to be made 

 by H. Wrightii, Cotteaii (not of Desor), " Echin. foss. Dep. Yonne," 

 p. 294, pi. xlii. ; the only differences being that that species 

 has broader, and consequently fewer, interambulacral plates, 

 that the rows of pores bordering the ambulacral areas are much 

 more flexuous, that the ambulacral tubercles do not alternate, 

 and that the spines are differently terminated at the base. From 

 most other species, such as H. Luciensis, D'Orb., H. intermedia, 

 Forbes, &c., the present form is distinguished both by its more 

 numerous interambulacral plates, and also at once by the small 

 and subequal size of the ambulacral tubercles, as well as by the 

 form of the spines where the latter are known. 



Hemicidaris Abyssinica — found rather abundantly in a bed 

 at the base of the Antalo limestone, close to the camp at Mai 

 Dongolo, four marches north of Antalo and three south of 

 Adigrat. Many of the specimens are in excellent order, and 

 the spines abounded in the bed, in some cases attached. Spines, 

 of the same species apparently, were met with here and there 

 throughout the Antalo limestone. 



