1865.] DUNCAN ASIATIC ECHINODERMATA. 363 



manensis, has a somewhat analogous relation to the other species of 

 its genus. The Holectypi flourished in Oolitic times, and have not 

 been found in strata higher than the Lower Chalk. Holectypus Ceno- 

 manensis is therefore a late species, and it departs somewhat from 

 the generic characteristics by having a fifth generative pore ; but, 

 unlike the Pygaster, it is a very variable species. The Salenia and 

 the Bpiaster belong to species which vary in Europe ; this is proved, 

 in the first instance, by the difference in the published types of the 

 species, and by comparing foreign with British specimens, and in the 

 second instance by M. Desor's determination that the variation in 

 the subanal projection of E. crassissimus is sufiiciently great to ren- 

 der E. distinctus a doubtful species, and that it is identical with 

 E. Varusensis. The species E. crassissimus and E. acutus have been 

 decided to be the same. In fact all these Epiasters are varieties of 

 a single type ; but which this may be, cannot be determined. They 

 are all found in the same strata in Europe. 



10. Conclusion.— Tha ferruginous nature of the strata containing 

 these fossils has been noticed. The iron is for the most part in the 

 form of a dull-red sesquioxide ; but here and there are traces of the 

 sulphuret. Some specimens of the rocks are hght in colour, and 

 consist of clayey limestone, very hard and with a fine texture. This 

 clay is the original matrix, the salts of iron and the fossils being 

 accidental deposits having mutual relations and forming the great 

 bulk of the strata. The fossils are usually well preserved, have been 

 but slightly rolled, were deposited in a soft clay, and, from the com- 

 parative absence of the sulphuret of iron and of the evidences of its 

 destructive mineralization, their details are generally very perfect. 



These observations on the nature of the deposits confinn the im- 

 pression produced by the study of the habits of the existing repre- 

 sentatives of the fossil forms in estimating the bathymetrical horizon 

 of the strata. The fossiliferous clays with Cidaris, with flat Echi- 

 noderms, Pectens, rugged Ostrece, Brachiopods, Bryozoa, and Eora- 

 minifera, could not have been deposited at a less depth than that in- 

 cluded in the NuUipore (Eo. VII.) zone of Forbes. Strictly speaking 

 they are not littoral deposits ; but when considered in relation to a 

 neighbouring very deep-sea or oceanic deposit, they may be so termed, 

 and thus accord with the well-known theory of Messrs. Godwin - 

 Austen and Daniel Sharp, that the Upper Greensands are littoral de- 

 posits in relation to the Lower White Chalk. Einally , it is consistent 

 with the harmony of nature that there should be a close connexion 

 between widely diffused species, their occasional persistency, their 

 more frequent tendency to variation, their range in depth and in 

 space, their belonging to a zone of sea-depth where there are great 

 facilities for emigration and difiusion, their entombment in the fine 

 calcareous clay of a sea-bottom removed from the regions where con- 

 glomerates and rocks can be formed, and their mineralization by a 

 pure oxide of iron. 



