FROM THE CORALLINE OOLITE. 



L27 



and by having secondary tubercles in the inter-ambulacra. From Pseudodiadema hemi- 

 spharicum it is distinguished by the primary tubercles in both areas being nearly of the 

 same size, and by there being fewer in each row; by the secondary tubercles being limited 

 to the poriferous side of the primary tubercles, and by the pores being arranged in double 

 pairs in the upper part of the zones. 



Locality and Stratigrapltical position. — This species is found in the Coralline Oolite 

 of Wiltshire, Oxfordshire, Dorsetshire, and Yorkshire. The finest specimens, however, 

 are those of Wilts, where they are sometimes admirably preserved. In Switzerland the 

 urchins which resemble our specimens have been collected from the " Terrain a Chailles," 

 of the valley of the Birse, of Blochmont, and of Weissenstein. 



[b. Pores unigeminal in the upper part of the zones.] 



Pseudodiadema hemisph/Emcum,* Agassiz. PL VIII, fig. 1 a, b, c, d, e,f. 



Cidarites pseudodiadema. Lamarck, Animaux sans Vertebres, torn, iii, p. 59, 



No. 17, 1st edit., 1816. 

 — — Deslongchamps, Encyclopedic Methodique, torn, ii, 



p. 197, No. 17, 1824. 

 Agassiz, Prodromus Mem. Soc. des Sciences Nat. 



Neuchatel, p. 22, 1836. 

 Agassiz, Prodromus Mem. Soc. des Sciences Nat. 



Neuchatel, p. 22, 1836. 

 Agassiz, Eclunodermes Fossiles de la Suisse, '2' partie, 



t. 17, figs. 49— 53, p. 11, 1840. 

 Desmoulins, Etudes sur les Ecbinides, p. 316, No 



1837. 

 Agassiz and Desor, Catalogue raisonne des Ecbinides 



Annales des Sciences Naturalles, 3 me serie, torn, vi, 



p. 349, 1846. 

 Lronn, Index Palseontologicus, p. 193, 1849. 

 Alcide d'Orbigny, Prodrome de Paleontologie Strati- 



graphique universelle, tome ix, p. 27 14 e etage, 



No. 423, 1850. 



dladema hemispi1.ericum. 



transversum. 



pseudodiadema. 

 Lamarceii. 

 dladema pseudodiadema. 



* M. Desor having selected the specific name "pseudodiadema," originally given by Lamarck to this 

 urchin, I have most reluctantly been obliged to adopt the name hemisphoericum, afterwards given by 

 M. Agassiz to the same species, iu order to avoid the double use of a specific name thus, Pseudodiadema 

 -pseudodiadema, Lamarck. This is one of the inconveniences arising from the modern practice of converting 

 specific into generic names, an innovation in nomenclature which cannot be sufficiently discountenanced, for 

 it leads, as in this case, to an injustice to the original describer of the species, whose name should always be 

 associated with the form he first described, and introduces, moreover, a further confusion into the 

 synonyms of species, a growing evil which every true naturalist should strive to the utmost to avoid. 



