80 Dr. T. Wright on Fossil Echinoderms 



ceolate at their upper fifth : the poriferous avenues are very nar- 

 row, and extend three-fourths of the distance between the apex 

 and the border : the pores in the avenues are only about one line 

 apart, and are united by short slits directed obliquely upwards 

 and inwards at nearly equal spaces apart from the base to the 

 apex ; the pores in the outer and inner series in each zone are 

 about the same size throughout : the narrowness of the poriferous 

 avenues forms a very important character in this species, by 

 which it is distinguished from an allied form, C. conoideus. The 

 interambulacra are of a triangular form ; the antero-lateral are the 

 smallest, and the postero-lateral and single interambulacrum of 

 about the same size are the largest : the apical disc is small, and 

 situated nearer the anterior than the posterior border, which 

 occasions a slight difference between the angle of inclination of 

 the anterior and posterior sides of the test : the centre of the 

 disc is occupied by a prominent button-like spongy madrepo- 

 riform body, around which the genital and ocular plates are 

 arranged, but their lines of suture can only be distinguished in 

 weathered specimens, or by removing the superficial layer of the 

 plates. The entire surface of both areas is covered with tuber- 

 cles, very much alike both as regards size, form, and irregularity 

 of arrangement ; the only parts exempt from tubercles are the 

 interporiferous septas of the avenues : the base is concave : the 

 mouth is situated in the centre of the disc, and is surrounded 

 by five large prominent lobes : the ambulacra form petaloid 

 depressions between the oral lobes, in which a number of pores 

 are clustered together in pairs. The anus is a large, transversely 

 oblong opening, placed immediately beneath the posterior mar- 

 gin ; from it to the mouth an elevated ridge of the test runs : the 

 single interambulacrum is slightly produced posteriorly where 

 the anus teminates : the tubercles are larger, and placed at 

 greater intervals apart on the base than on the dorsal surface : 

 the marginal fold of the test forms an acute angle, and on the 

 border thereof the tubercles are clustered closer together in 

 greater numbers, with smaller interspaces between them, than in 

 any other part of the skeleton. 



Affinities and differences. This species very much resembles 

 in form and size C. conoideus, but it is readily distinguished from 

 it by the following characters : the ambulacral areas are smaller, 

 the poriferous zones are narrower, and the outer and inner pores 

 of each pair are nearly of the same size, whilst the septas between 

 the pores are thicker; the dorsal surface is not so much ele- 

 vated, the base is concave, the anus is large and transversely 

 oblong, and the mouth possesses very prominent oral lobes. 



Locality and stratigraphical range. This Urchin was collected 

 at Malta, from bed No. 2. The tine specimen before us belongs 



