Dr. T. Wright on the Cassidulidse of the Oolites. 311 



The middle part of each petal forms a slight ridge ; on the con- 

 trary, the five corresponding marks on the base meeting in the 

 mouth are depressed. The base is concave. The mouth is situ- 

 ated immediately under the vertex. The vent is in a short groove, 

 on the edge, but more towards the upper surface, as in some of 

 the Spatangus family." 



Affinities and differences. — The marginal position of the anal 

 valley forms a sufficient diagnosis between A 7 , emarginatus and 

 its congeners, but the want of a specimen prevents us making a 

 comparison between it and them ; the petaloidal ambulacra and 

 position of the anus bring this Urchin into near affinity with 

 the genus Pygurus. 



Locality and stratigraphical range. — It is found in the Coral- 

 line Oolite of Malton and Scarborough, and is said to be rare. 



History. — This Urchin has been figured by Messrs. Young and 

 Bird and by Mr. Phillips, but described by neither. Prof. Forbes 

 has drawn up a good diagnosis of the species, but a detailed de- 

 scription is now a desideratum. 



In the ' Catalogue raisonne des Echinides ' of Agassiz and 

 Desor there is a species entered under the name of Clypeus ri- 

 mosus, described as "Espece plate, discoide, a ambulacres cos- 

 tales," and stated to be from the Oolitic strata of Gloucestershire, 

 and in the collection of M. Deluc ; we know of no such species 

 from the Oolites of this county, and suspect that it may probably 

 be one of the many varieties which N. sinuatus presents in our 

 different beds. There is a small Nucleolite in the British Mu- 

 seum from the Great Oolite of Harleston, apparently distinct and 

 allied to N. clunicularis ; in the same collection there is another 

 small species from the Inferior Oolite of Stroud which is probably 

 new*. 



In Prof. M'Coy's paper "On some new Mesozoic Radiataf/' 

 there are two species described under the names of N. planulatus 

 and N. aqualis, neither of which we know ; the former is said 

 to resemble N. planatus of Roemer, and the latter N. latifrons 

 (latiporus ?), Agassiz, which is only an orbicular variety of N. clu- 

 nicularis from the Cornbrash. 



A careful comparison of these forms, with other typical spe- 

 cies and the varieties thereof, is very desirable, as the creation of 

 new species from transitory forms retards rather than advances 

 palaeontology. 



Genus Pygurus, Agassiz. 



Test discoid or ovoid, more or less elevated ; anterior border 

 flattened, posterior border rostrated ; ambulacra having elegant 

 petaloid forms ; poriferous zones very large in the centre, much 



* Prof. Forbes, M< m. Geol. Sun-. Decade 1. pi. 9. 

 t Annals of Nat. Hist. vol. ii. Second Series, p. 416. 



