312 HOLASTER 



in those from the Upper Greensand it has entirely disappeared, whilst on some speci- 

 mens from the Lower Grey Chalk and the Chloritic Marl, its true character may be 

 studied. Fig. 1/ shows an enlarged portion of a test, in which the granules existed 

 with several of the primary tubercles interspersed at irregular intervals in the midst of 

 the granulation. Many of the tubercles are raised on finely crenulated bosses, which 

 support small perforated tubercles, accurately drawn in fig. 1 /. 



Affinities and Differences. — The general form of the test varies much in this species, 

 being more or less depressed or elevated in different examples ; still the other characters, 

 which may be considered as specific, remain very permanent in all these variations. The 

 examples collected from the Grey Chalk near Folkestone, and from the Lower Chalk of 

 Sussex, are in general larger and better preserved than the small typical specimens 

 collected from the Upper Greensand at Chute Farm, Wilts. The Chalk specimens have 

 likewise retained many of the large primary tubercles surrounded by patches of the 

 granulated surface, and specimens collected from our Lower Chalk are absolutely 

 identical with a specimen I have from the Craie Chloritee of Cap-le-Heve, near Rouen. 



After a careful comparison between the tests of Hoi. Icevis and those of Hoi. 

 carinatus, and good figures of Hoi. transversus and Hoi. marginatus, I agree with my 

 learned friend, Monsieur De Loriol, 1 that they in reality are all so many varieties of Hoi. 

 IcBvis, grown under different physical conditions, which have changed only some of the 

 external characters of their original form, but left the essential and specific ones 

 untouched. De Loriol has examined likewise the original example of the true large Hoi. 

 Sandoz, Agass., contained in the Museum of Zurich, with other examples of the collection 

 of Monsieur Du Bois de Montpereux, found by him in the Upper Greensand of Souaillon 

 (Neuchatel), and De Loriol affirms that Hoi. Sandoz is only a very large and very fine 

 specimen of Hoi. Icevis. Mons. De Loriol unites also Hoi. Trecensis, Leymerie, with 

 Hoi. Icevis. In PI. LXXIV, fig. 2, I have given a very good figure of this species, and 

 in page 324 have entered fully into this subject when describing its affinities. Holaster 

 Icevis differs from Hoi. planus, Mantell, in some particulars. In Hoi. planus the test is 

 larger, more oblong and less cordate, and the ambulacral summit subcentral nearer the 

 anterior border ; the upper surface is flat and declines very little towards the posterior 

 border, which is only slightly truncated to form an anal area, in the upper part of which 

 the vent opens. Hoi. Icevis resembles likewise Hoi. suborbicularis in some points of 

 structure, but differs so widely in others that I must refer to my article on that species, 

 and to that on Hoi. subglobosus, for the affinities and differences existing between them. 



Locality and Stratigraphical Position. — The small figured specimen I collected 

 from the Upper Greensand at Chute Farm, Wilts, where it is very common. The 

 tests are so much covered over with adhering sand particles that it is rare to obtain a 

 good specimen. I have collected this species likewise from the Grey Chalk near Folke- 

 stone, and from the Lower Chalk, near Lewes, Sussex. 



1 ' Echinologie Helvetique,' p. 324, 1873. 



