C. D. 8herhorn — Hipponyxfrom the White Chalk. 437 



and base unknown. Irregularly covered with tubercles, the growing 

 margin of the shell having taken up the natural markings of the 

 Echinoid to which it had attached itself. 



Type. — Gr. E. Dibley Collection, on a large Micraster cor-hovis from 

 the TerehratuUna zone of Cuxton, Kent. This specimen has two 

 delicate tubes running across it, probably foraminiferal. Fig. 1, X 2 

 and Fig. 3, X 4, the latter showing the ornament. Apparently another 

 specimen of this form is in Dr. Blackmore's collection, and comes from 

 the mucronata Chalk of Clarendon, near Salisbury, but it is too crushed 

 to allow of any definite description by me. 



There is also evidence of a third species in which the ornament on 

 the ribs is imbricate, but the fragment (in Dr. Blackmore's collection, 

 from the mucronata Chalk of Alderbury) is not sufficient for descriptive 

 purposes. 



Dr. Blackmore's specimens are all too delicate to take casts from, 

 but Mr. Dibley's specimen {H. dibleyi) is so well supported by chalk 

 inside, and so firmly attached to the shell that Mr. F. 0. Barlow, the 

 skilful formatore of the British Museum (Nat. Hist.), has been able 

 to take an exact cast for the National Collection by means of wax 

 squeezes. 



Fig. 1. — Hippomjx dibleyi, n.sp. ; x 2; from the TerehratuUna zone of Cuxton, 

 Kent. 

 ,, 2. — Hipponyx blachmorei , n.sp. ; x 2 ; from the Actinocamax quadratus zone 



of East Harnham, Salisbury. 

 ,, 3.— Part of Fig. 1 [H. dibleyi) ; x 4. 



