from the Island of Malta. 113 



prominent convex elevations of the test, which arc bounded 

 by wide poriferous avenues, composed of two series of simple 

 pores united by oblique grooves ; the internal series of pores are 

 round, the external series are elongated transversely in the 

 direction of the grooves ; the pores at the end of the avenues 

 are much more so than those of the summit ; the apical disc 

 is small, and occupies the centre of the dorsal surface, lying in 

 a slight depression formed by the bending-in of the summits of 

 the areas ; those of the single area, and the antero-lateral and 

 postero-lateral areas of the left side, being rather more pro- 

 minent than those of the right side of the test. The madre- 

 poriform body occupies the w hole surface of the disc, the ocular 

 and genital ])lates being quite indistinguishable from the general 

 structure of the test ; the five genital pores pass obliquely into 

 the interior, at a short distance from the disc. 



The base is flat, and the mouth lies in a very deep depression 

 in the centre of the under surface ; the opening is pentagonal, 

 its wide w^alls being formed by the incurving of the basal por- 

 tions of the areas ; from each of the angles of the pentagonal 

 opening, a deep furrow^ passes outwards towards the margin of 

 the test, and becomes continuous with the median suture of the 

 ambulacral areas. The jaws are absent in all the specimens we 

 have examined. The anus is a small round aperture, situated 

 near the posterior margin of the base of the test; in some 

 specimens it is elongated in the transverse diameter, and 

 measures about /^ths of an inch across. The tubercles are 

 nearly of the same size on the upper surface, and their summits 

 are level with the test, so that the areolas which surround them 

 are excavated out of the superficial layer of the calcareous plates. 

 The intertubercular surface is ornamented with a microscopic 

 granulation, disposed in circles around the areolas of the tu- 

 bercles, and filling up all the intervening spaces. The tubercles 

 at the base are larger and moi'e closely set together than those 

 on the dorsal surface ; a row^ of five or six tubercles is seen on 

 each of the interfissural bands of the poriferous avenues. 



Affinities and differences. — C. alius has many traits in common 

 with C. rosaceus. In the genex"al outline, in the size, form and 

 extent of the ambulacral areas, there is much resemblance ; but 

 the campanulate form of the dorsal surface, the smallness of the 

 apical disc, and the truncature of the posterior border constitute 

 differences which may be traced through all the varieties 

 C. altus assumes. The thickness of the marginal fold, and the 

 great development of the ambulacral flower, when compared 

 with the thinness of the border and the limited extent of the 

 ambulacra, distinguish at a glance C. altus from C. Tarbellianus, 

 C. marginatus, and C. scutellatus. The dome-shaped upper 



Ann. ^ Mag. N. Hist. Ser. 2. Vol. xv. 8 



