FROM THE INFERIOR OOLITE. 363 



Clypeus which was communicated to him by Dr. Heucher from the Royal Cabinet of 

 Dresden ; this urchin was described by Leske* in his additions to Klein's Monogragh as 

 a distinct species, under the name Clypeus sinuatus ; by subsequent authors, C. Plotii, Klein, 

 with the author's reference to Plot's figure as the type of the same, is omitted. Although 

 Leske described both species and pointed out the diagnostic differences which he supposed 

 to exist between them, nevertheless Klein's reference to the type of the English species has 

 been overlooked, and Leske's name given to this urchin. Lamarckf introduced still further 

 confusion into the subject by describing the flattened varieties of Clypeus Plotii, Klein, 

 under the name Galerites patella, and this new specific synonym was adopted by Defrance, J 

 Deslongchamps,§ De Blainville, II and Agassiz,^ and is retained by most Continental 

 palaeontologists at the present time. As it has been one of my objects to trace the 

 true history of every species described in this work, even at the risk of disturbing a 

 name which has passed unchallenged for nearly a century, justice to Klein renders 

 it imperative that his name should be retained to the urchin which was first figured 

 by Dr. Plot, and that of Clypeus sinuatus, Leske, to the specimen contained in the 

 Dresden collection ; should a farther examination of that urchin show that it is only 

 a tumid variety of C. Plotii, Klein, the priority of the latter will still entitle it to be 

 retained as the name of this species. 



Although this large buckler-shaped urchin has been well known to naturalists for 

 nearly two centuries, nevertheless no good figure of the test, with details of its structure, has 

 been given until now ; this is the more remarkable, when the beauty and abundance of the 

 species is considered, together with its importance in Oolitic geology. 



The test exhibits many varieties of form and outline ; some of these have received specific 

 names and descriptions by different authors, of which Clypeus angustiporus, Agass., and 

 CI. excentricus, M'Coy, are examples. This urchin attained its most typical form and 

 best development in the seas which deposited the beds constituting the zone of Ammonites 

 Parkinsoni of the Inferior Oolite ; the specimens found in the Stonesfield Slate, Great Oolite, 

 and Cornbrash are in general smaller, and deviate more or less from the Inferior Oolite forms. 



The ambulacral areas on the dorsal surface are narrowly lanceolate ; the anterior pair, 

 and single area, are about the same width ; but the posterior pair are wider ; they are all 

 more or less slightly flexed (PL XXVIII, fig. \ a) ; at the base they form narrow 

 depressed bands, which radiate from the mouth to the circumference (fig. 1 h), and give 

 a stellate character to the base of the test. 



* ' Additamenta ad Kleinii Disposidoiiem Echinodermat 



■f 'Animaux sans Vertebres,' torn, iii, p. 23, No. 14. 



X 'Diction, des Sciences Naturelles.' 



§ ' Ecyclop^d. Methodique.' 



II 'Diction, des Sciences Naturelles.' 



^ ' Echinodermes Fossiles de la Suisse.' 



