OF WESTEEN SIND. 139 



Locality. In the Khirthar series of strata ; three or four miles south of Trak 

 Hill, Survey-number -[247- 



Illustrations of the Species in Plate XXV. 

 Figs. 1-8. Abactinal view of a series of specimens, to show the variations of the . mar- 

 ginal outline : natural size. 

 9. Abactinal view of the test of the same specimen as Fig. 8 : magnified 2| times. 



10. Actinal view of the same specimen : magnified 2^ times. 



11. Longitudinal profile of the same specimen: magnified 2-| times. 



12. Apical disk and surrounding portions of the test: magnified. 



13. Peristome and surrounding portions of the test : magnified. 



Suborder ATELOSTOMATA. 

 Family CASSIDULIBJE. 



Subfamily ECEINONEINM. 



Oenus AMBLYPYGUS, Agassiz, 1840. 



Test of large size ; marginal contour subcircular or ovoid, more or less convex above 

 and concave beneath, with thick margins. 



Apical summit subcentral. Apical disk small and compact; four generative 

 and five ocular pores ; the madreporiform body occupying the whole of the central 

 portion. 



Ambulacra petaloid, widely open at the outer extremity, reaching nearly to the 

 margin. Poriferous zones with the inner pores round and the outer pores elongate, the 

 pairs united by a conjugating furrow. The extrapetaloid ambulacral plates are each 

 punctured by a pair of very minute pores, placed diagonally and close together ; and 

 this extrapetaloid portion of the poriferous zone forms a straight, narrow, simple line 

 of pores, often scarcely visible at the margin, extending to the peristome. 



Peristome subcentral, oblique, subpentagonal, with irregular sides. 



Periproct very large, oval or pyriform, with the major diameter in the direction of 

 the longitudinal axis of the test, situated between the peristome and the posterior 

 margin. Ornaipentation very homogeneous. Tubercles very small, crenulate and 

 perforate, placed in scrobicules uniformly distributed over the surface of the test, the 

 intermediate space being occupied by fine miliary granulation. 



This genus is nearly related to EcMnoneus, as we have shown in the " Description 

 of the Fossil Echinoidea of Kachh and Kattywar " (Pal. Ihd. ser. xiv.). The oblique 

 peristome, the size and position of the periproct, and especially the structure of the 

 ambulacral plates, with the continuous series of double pores, indicate unquestionably 

 a much closer alliance than has hitherto been recognized between the two genera. 

 In the work just noticed we have discussed at length the various species hitherto 

 included in the genus Amhlypygus. The species from Kachh, along with the present 

 series from Sind, constitute a remarkable assemblage of forms. 



