874 CLYPEUS. 



Affinities and differences. — Chjpeus Millleri more closely resembles Clypeus Plotii than 

 any other English species ; having affinities Math it in the form and structure of the 

 ambulacra, the extent and narrowness of the anal valley, and the depression of its dorsal 

 surface. It is distinguished from C. Tlotii, however, by its oblong figure, truncated 

 posterior border, shorter and more graceful petaloidal ambulacra, finer and more minute 

 sculpture on the plates, a flatter base, with smaller tubercles thereon. The large specimen of 

 Chjpeus Millleri (fig. 1) very much resembles Clypeus Michelini, but the widely petaloidal 

 character of the ambulacral areas in the former species present a great contrast to the 

 structure of the homologous portion of the test in the latter urchin, and serve to distinguish 

 them from each other; whilst the depression of the dorsal surface, the narrowness of 

 the anal valley, the smallness of the apical disc, and the microscopic sculpture on the 

 test, assimilate the two forms closely together. 



It is distinguished from Clypeus Solodurinus, Ag., by having a much flatter under 

 surface, with inconsiderable undulations of the inter-ambulacra ; whilst, according to 

 Agassiz, in the Swiss urchin, " La face inferieure est regulierement ondulee par suite de la 

 depression des ambulacres." The test in C. Millleri is likewise extremely thin, the 

 sculpture fine, and almost microscopic ; whilst in C. Solodurinus, " Le test est assez epais, 

 et reconvert d'une granulation assez uniforme sur toutes les parties intactes.^' 



Locality and StratiyrapMcal position.- — I collected this Clypeus from the white 

 marly vein which traverses the upper region of the Great Oolite in some parts of 

 Gloucestershire, as near Cirencester, near Northleach, at Salperton tunnel. Great Western 

 Railway, near Minchinhampton, and near Cowley Wood ; in all these localities it was 

 associated more or less abundantly with Ecliinohrissus Woodwardi, Wr. Mr. Frederick 

 Bravender collected the fine large specimen figured in PI. XXXIII, fig. 1, from the Eorest 

 Marble near Cirencester. The Rev. A. W. Griesbach found one specimen in the Corn- 

 brash of Rushden, Northamptonshire, where it is extremely rare, as the specimen which 

 my kind friend has communicated is the only one he has seen in that locality. 

 M. Bouchard-Chantereaux sent me a specimen which he collected from the Great Oolite 

 near Boulogne-sur-Mer. 



History. — This urchin was first discovered by Mr. S. P. Woodward, in the Great 

 Oolite near Cirencester ; it was subsequently described in my memoir on the ' Cassidulidse 

 of the Oolites ' as Nucleolites Solodurinus, and is now figured for the first time as Clypeus 

 Millleri. I dedicate the species to the memory of Johannes Miiller, late Professor of 

 Physiology in the University of Berlin, whose profound observations on the anatomy, 

 physiology, and metamorphoses of the Echinodermata have thrown so much new and 

 important light on the natural history of this class of the Animal Kingdom. 



