OF WESTEEN SIND. 319 



Or^^r ECHINOIDEA EXOCYCLICA. 



Suborder GNATHOSTOMATA. 

 Family GLYPEASTRIDM 



Subfamily EUGLTPEASTRIN^. 



Genus CLYPEASTER, Lamarck, 1801. 



The types of MM. d'Archiac and Haime's Clypeaster profundus and C. Halaenis, 

 which are preserved in the collection of the Geological Society of London, are worthless, 

 weather-worn specimens upon which it is scarcely possible to base any critical determi- 

 nation. They are valueless in a case of specific comparison, and we shall therefore not 

 attempt one in the present instance. 



Amongst the great number of examples of Clypeaster obtained by the Survey 

 from the Gaj strata in Sind, there is a large series which we consider to belong to one 

 species, notwithstanding the excessive amount of variation occurring within its limits. 

 The study of the recent species of Clypeaster has taught us how great the modification 

 of external form in this group may be ; and it is therefore not astonishing to find a 

 similar plasticity of habit in the series of fossils referred to : although in the present 

 instance it is carried to such a degree that scarcely two examples precisely alike could 

 be selected from a series of over fifty specimens. 



It is our opinion that the two species of d'Archiac and Haime referred to above, 

 are both immature forms, which would take their place in the series under notice, if 

 the types were good enough for comparison. On these grounds we propose to describe 

 the mature, and what seems to us characteristic, form of the series in question under 

 the name of C. profundus, solely from our wish to avoid multiplying names unnecessarily 

 and our unwillingness to rob our illustrious predecessors of one link in the chain which 

 binds their names to posterity, 



1, Clypeaster profundus {d'Archiac), Duncan 8f Sladen. Plate L, Figs. 1-4. 



Marginal contour subpentagonal with the angles rounded, longer than broad in 

 the proportion of 1 : 0"913. The greatest breadth is opposite the termination of the 

 antero-lateral petals ; the lateral sides are very faintly incurved as they contract towards 

 the posterior end, whilst the margin of the odd posterior interradium is rather more 

 decidedly incurved. At the margin the test is very thin, and more or less undulating 

 in consequence of being slightly tumid in the prolongation of the radial areas ; the 

 abactinal surface passes from the margin with a very gentle slope at a small angle 

 of declivity, until it reaches the extremity of the ambulacral petals, where it rises 

 abruptly to form an arched dome of considerable elevation, which comprises the whole 

 region of the petals. Seen in longitudinal profile, the posterior declivity of the dome 



