8 



BRITISH FOSSILS. 



and graduates very gently into 14 on the one side, and the normal cor- 

 anguinum on the other. 



Agassiz and Desor (whose declaration that forms are specifically 

 identical is pretty good warrant for considering them undistinguishable) 

 identify with this form 



16. Spatanyus anancliytoides, Desraoulin, and, 17, Micraster latus, 

 Agassiz (Cat. Syst.) and Sismonda, whose figure represents the spe- 

 cimen only from above. It is fair to say that the Italian author, in the 

 " Memoir on the Fossil Urchins of Nice," distinguishes his latus from 

 yibbus, referring the latter name to both Lamarck and Goldfuss. He 

 inserts Risso's Spatanyus suh-alpinus as a doubtful synonym of latus. 

 From the view which Sismonda, in the very excellent memoir cited, 

 one of the best papers on fossil Echinoderms with which I am ac- 

 quainted, takes of the specific distinctions of Micrasters, in all probability 

 his latus should claim only to rank as a sub-variety under the form 

 yibhus of cor -anguinum. 



Thus seventeen forms, at fewest, — I fear more might be added, — 

 have been at difi*erent times regarded as distinct species ; all of which 

 appear to be variations (many not even so much) of a single specific 

 type. In the Catalogue Raisonne des Echinides " the authors hold 

 out of the number, six specific types of Micraster^ viz., cor-anyuinum, 

 Michelini, acutus, cordatus, brevis, and yibbus. But how acutus and 

 Michelini are to be separated from cor-anyuinum it is difficult to under- 

 stand ; whilst that cordatus (better known in England under the name of 

 rostratus) is a variety of cor-anyuinum, few collectors even will be 

 inclined to dispute. As to the form called brevis, it is constantly 

 regarded in England as a variety of cor-anyuinum, and most certainly, 

 as I have already said, passes into the normal type on the one hand, and 

 into the extreme yibbus on the other, by almost imperceptible grada- 

 tions. 



British Localities and Geoloyical Ranye. — Chalk. It is found in 

 all the chalk districts of England ; abundantly in many counties, as in 

 Kent, Sussex, and Norfolk. Its geological position is usually in the 

 upper chalk ; it is recorded also from the lower chalk of Pinhay and 

 Charlton. The normal and rostrated forms are most common ; the sub- 

 gibbous variety is next, and the extreme gibbous one rarest. Portlock 

 records it from the chalk of Magilligan, county Derry, in Ireland. 



It is said to occur in the green-sand of Devon, but this is probably a 

 mistake. 



Foreiyn Distribution — In the chalk of France, Germany, Switzerland. 

 Sismonda finds it in the marly chalk in the neighbourhood of Nice. 

 Agassiz records the sub-gibbous variety from the chalk marl of Nor- 

 mandy, &c. ; from the " Craie chloritee of Coudrecieux (Sarthe) ;" and 

 from the chalk with Hippurites of Nice. 



