154 THE FOSSIL ECHINOIDEA 



There is no development of a true phyllode, although a slight tendency exists 

 to form an inner series of pores, caused by the stepping out of an occasional pore here 

 and there from the normal uniserial rank. The transverse diameter of the peristome 

 measures about 8 millim., and the longitudinal 5 millim. 



The periproct is very large, subtriangular in outline; the outer margin, which 

 forms the base of the triangle, being a gentle curve, the inner margin beipg bounded 

 by two very slightly curved lines, which form the sides of the triangle, the apex 

 directed towards the peristome, and the lateral angles being sharp. The periproct is 

 entirely on the under surface, close to the margin, and, being situated on the slight 

 outward slope of the ventral tumidity, its plane is directed slightly upwards. The 

 shorter diameter of the aperture, which corresponds with the longitudinal axis of the 

 test, measures 6"5 millim., and the transverse diameter 12 millim. 



BemarJcs. This species is, perhaps, most nearly allied to E, discoideus, d'Archiac ; 

 but is distinguished from that form by its higher test, its subconoidal abactinal surface, 

 and its higher and more tumid margins. It is further distinguished by the slightly 

 tumid interporiferous areas and the distinctly petaloid outline of the ambulacra, the 

 former in E. discoideus being flush with the test, and the latter almost as completely 

 open as in Conoclypews. In E. discoideus the actinal surface is described as " sub-plan," 

 and the periproct small and fairly regularly elliptical. In these points this species is 

 very diflerent. We know of no other form with which E. rotunda can be confounded. 



There is a crushed specimen which is larger and more elongate than the type, and 

 in which the actinal surface appears to be somewhat less tumid ; but this is, perhaps, 

 owing to the damage it has sustained. In all points of detail it accords fully with the 

 type we have described. 



Bimelfisions. 



a. b. e. 



Tnillim. millim. milli m. 



Length of the test 58 58-5 67 



Breadth of the test 55 54*5 (broken) 60-5 



Height of the test 34 34 27-5 (crushed) 



Breadth of postero-lateral petal . 8'50 8'50 8*80 



„ of antero-lateral petal . 7*40 7'40 8 



G-226 

 103 



Locality. In the Khirthar series: Eiver-section, east of Trak. Survey-number 



Illustrations of the Species in Plate XXVIII. 

 Fig. 1. Abactinal view of the test : natural size. 



2. Actinal view of the test : natural size. 



3. Longitudinal profile of the test: natural size. 



4. The apical disk : magnified. 



5. A portion of a petal, about midway between the extremity and the apex : 



magnified. 



6. The peristome and surrounding portions of the test : magnified. 



