6 



BRITISH FOSSILS. 



The very great variation of outline, tumidity, and consequent arrange- 

 ment of the ambulacra, have caused this Micr aster to be split up into nu- 

 merous spurious species. But in the collections of the Geological Survey, 

 and in many private collections, especially those of Mr. Bowerbank and 

 Mr. Wetherell, where extensive suites of specimens are assembled, and 

 intermediate forms as carefully preserved as extreme ones, it becomes 

 very manifest that all resolve themselves into one species, sufficiently 

 marked by constant characters common to all the individuals. I have 

 grouped them under three conspicuous types — normalis, rostratus, and 

 gibhus ; but as the variations of each of these have been honoured by 

 not a few palaeontologists with specific rank, I think it best to enumerate 

 all the forms which have been so distinguished. 



A. " Species " constructed out of the Normal form, 



1. Cor-anguinum, Auctorum. The old figures in Leske's edition of 

 Klein (tab. xxiii., figs. A, B, C, D), are bad representations of the or- 

 dinary aspect of what is placed in collections under this name. The 

 figure of cor-anguinum, Goldfuss (Pet. Germ., tab. xlviii., fig. 6), is 

 perhaps the best representation of one of the most common varieties of 

 what is regarded as this species by all authors. Parkinson's Spatangus 

 cor-marinum (Org. Rem., iii., pi. 3, fig. 11), represents a specimen 

 with deeper ambulacra than usual. The cor-anguinum of Woodward's 

 " Geology of Norfolk" is var. gihbus. 



2. Spatangus cor-testudinarium. Goldfuss (tab. xlviii., fig. 5) ; Mi- 

 craster cor-testudinarium of Agassi z (Cat. Syft.) ; but more lately (in 

 the Catalogue Raisonne) considered by Agassiz and Dasor as " var. 

 lata " of their restricted Micr aster cor-anguinum. This is only a very 

 slight variety of the normal form, constructed out of such specimens as 

 have the mouth slightly further back than usual, a feature not unfre- 

 quently seen in depressed specimens. According to Agassiz, the name 

 " Spatangus anticus " of Defrance applies to this form. 



3. Micr aster arenatus of Agassiz (Cat. Syst.), since referred by 

 Agassiz and Desor to their variety " major'' of their cor-anguinum., to 

 which variety they refer the figure and description of " Micraster are- 

 natus,^^ in E. Sismonda's " Memoria sugli Echinidi Fossili del contrado 

 di Nizza" (p. 28, tab. i., fig. 2). In the plate in question, however, no 

 profile of this urchin is given, and the description of the elevation of 

 the back^ would seem rather to indicate a variety of the gihbus or ros- 

 tratus types. F. A. Roemer, in his " Versteinerungen des Nord- 

 deutschen Kreidegebirges," identifies arenatus with " rostratusJ^ 



4. Micraster Michelini of Agassiz (in the Catalogue Raisonnee). 

 This is the cor-anguinum of Agassiz, in his "Description des Echino- 

 dermes Fossiles de la Suisse" (tab. iii., figs. 14, 15) ; in which work he 

 identifies it with the cor-anguinum of previous authors. In his later 



