222 THE FOSSIL ECHINOIDEA 



The peristome is very excentric in front ; the regions of the ambulacra on the 

 actinal surface are conspicuously naked ; and the actinal plastron is more or less tumid, 

 and becomes gibbous at the culminating point posteriorly. The figure of the abactinal 

 surface given on the Plate is considerably restored from a very badly crushed example, 

 the detail of which is only preserved fragmentarily. 



There are two fascioles present — a peripetalous and a latero-subanal. The peri- 

 petalous fasciole is broad, and closely embraces the ambulacral petals, crossing the 

 anterior interradia at a short distance external to the apparent bifurcation of the 

 gibbous keel, and bisecting the groove of the odd anterior ambulacrum just before the 

 rounding of the anterior margin commences. The lateral fasciole is a very thin, narrow 

 band, which joins the peripetalous fasciole behind the extremity of the antero-lateral 

 petals, crosses the lateral interradia through the two uppermost prominent gibbosities, 

 and passes thence beneath the periproct, traversing the inferior margin of the concave 

 area. 



The ornamentation on the abactinal surface is uniformly small, excepting along 

 the inner flanks of the keels which bound the odd anterior groove, where some larger 

 tubercles are present. On all the gibbose plates of the interradia the tuberculation is 

 smallest at the summit of the prominence, and increases in size as it recedes therefrom. 

 All the ornamentation increases in size and in distance apart as it approaches the 

 ambitus, especially in the anterior region ; and the primary tubercles become larger 

 and widely spaced on the margins of the actinal surface. On the actinal plastron a 

 more or less definite arrangement of lines radiating from the culminating point is 

 maintained ; the size of the tubercles increasing as they approach the peristome, those 

 near the culminating point being the smallest. 



Bemarks. It is not without hesitation that we have ranked this form as a 

 Schizaster — the subcentral apical disk, the comparatively divergent anterior petals, 

 and the rather long posterior petals being abnormal for the genus. On the other 

 hand, the deeply excavated ambulacra, the carinate keels of the interradia, the 

 character of the ornamentation, and of the apical disk are all more clearly allied to 

 Schizaster than to Linthia ; and we have consequently placed the form in accordance 

 with what seem to us the sum of its afiinities. In sequel to these remarks it is 

 interesting to note that 8. symmetricus has rather a strong resemblance to Linthia 

 Navillei, described bydeLoriol from Egypt, in so far as the shape of the test is 

 concerned ; but the Indian species diffiers in being more depressed, in the shorter and 

 more precipitous truncation, in the depth and character of the ambulacral grooves, 

 and in the more excentric apical disk. We know of no species with which it can be 

 confounded, and it is very distinct from the other Indian forms. 



Dimensions. Length of test 30-5 millim., breadth 28 millim., exact height inde- 

 terminable. 



Locality. In the Khirthar series of strata : Eight or nine miles south by west of 

 Jangri, and east of the Surjana range. Survey-number ?^^, 



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