FROM THE STONESFIELD SLATE. 75 



Affinities and differences. — This species closely resembles Hemicidaris granulosa in the 

 presence of granules instead of tubercles, on the upper part of the test. It is distinguished 

 from it by the following characters : the form is more conoidal, the ambulacra are wider, 

 the granules on the same are smaller and more numerous ; the scrobicular circles are 

 incomplete, and the surface of the plates of the apical disc is covered with granules. 

 Hemicidaris piistulosa resembles Hemicidaris Stokesii (PI. Ill, fig. 3) in the sudden 

 diminution in the size of the tubercles on the upper parts of the inter-ambulacral areas, 

 and in the granulated character of the surface of the apical disc ; but it is distinguished 

 from that species in having unequal-sized, irregularly disposed marginal granules on the 

 ambulacral areas. The tubercles of the two upper inter-ambulacral plates in Hemicidaris 

 Stokesii are perforated, with distinct scrobicular circles around their areolas (PI. Ill, 

 fig. 3 a) ; whereas in Hemicidaris pustulosa the rudimentary tubercles and the scrobicular 

 granules form clusters on the plates (PI. Ill, fig. 1 a). The elements of the apical disc, 

 in both species, are much alike in form, structure, and sculpture. The disc, however, in 

 Hemicidaris Stokesii does not rise above the surface ; whereas in Hemicidaris pustidosa it 

 forms a marked projection. There is no other Oolitic species of Hemicidaris at present 

 known for which Hemicidaris piistulosa can be mistaken. 



Locality and Stratigraphical position. — The only English specimen I have seen was 

 presented to me by my excellent friend Mr. Etheridge. The exact locality in Dorset- 

 shire from whence it was collected, however, is not known ; but, judging from the litho- 

 logical character of the rock in which it is imbedded, it is probable it came from the Inferior 

 Oolite near Bridport. 



The French specimens were found in the " Grand Oolite (Bathonien), de Luc, St. 

 Aubin, Langrune, Calvados." — Deslong champs. 



History. — This species was first entered in the ' Catalogus Systematicus' of Agassiz, 

 and afterwards in the ' Catalogue raisonne' of Agassiz and Desor, but it is now figured 

 and described for the first time. 



B. Species from the Stonesfield Slate, Great Oolite, Bradford Clay, Forest Marble, 

 and Cornbrash.-=Wth JEtage, Bathonien, d'Orbigny. 



Hemicidaris Stokesii, Wright, nov. sp., PI. HI, fig. 3 a, b, c. 



CiDARis FROM Stonesfield. Stokes, Transactions of the Geological Society of London, 



2d series, vol. ii, pi. 45, fig. 17. 



Test circular, depressed ; ambulacral areas straight, with two rows of small regular 

 marginal tubercles ; inter-ambulacral areas with large primary tubercles at the equator. 



