FROM THE INFERIOR OOLITE. 173 



The Pedinas are all extinct, and appear to be limited to the Oolitic rocks. One 

 species is catalogued with doubt as coming from the Cretaceous formation. 



Pkdina rotata, Wright (non Agassiz). PL XIII, fig. 1 a, b, c, d, e. 



Echinus lineatus. Murchison, Geology of Cheltenham, 2d edit., p. 73 (1845). 

 Pedina rotata. M'Coy, Annals and Magazine of Natural History, 2d series, vol. ii, 



p. 20 (1848). 

 — — Wright, Annals and Magazine of Natural History, 2d series, vol. viii, 



p. 273 (1851). 

 Echinopsis rotata. Forbes, in Morris's Catalogue of British Fossils, 2d edit., p. 78 (1854). 



— — Salter, Memoirs of the Geological Survey, Decade V, pi. 3 (1856). 



Pedina rotata. Cotteau, Etudes surles Echinides Fossiles, p. 315 (1856). 



Test circular, or sub-pentagonal, with tumid sides, more or less depressed ; ambulacral 

 areas narrow, furnished with two marginal rows of small, numerous (from twenty-five to 

 thirty in each row,) close-set, equal-sized tubercles, arranged with great regularity through- 

 out ; and two inner rows of minute tubercles, which disappear above and below ; inter- 

 ambulacral areas wide, with two rows of primary, which extend without interruption from 

 the mouth to the disc, and four rows of secondary tubercles on their outer side, which 

 disappear at the equator ; mouth opening small, peristome decagonal, with deep notches 

 and unequal-sized lobes, apical disc of moderate size, genital plates nearly equal, poriferous 

 zones wide, trigeminal ranks oblique, with two granules between each rank. 



Dimensions. — Height, seven tenths of an inch ; transverse diameter, one inch and four 

 tenths. 



Description. — There is much difficulty in distinguishing by good characters the different 

 species of Pedina figured by M. Agassiz in his ' Echinodermes Fossiles de la Suisse,' 

 arising in a great measure from the thinness of the test, the delicacy of its sculpture, 

 and the great similarity which prevails among the different species of this group ; the 

 absence of good details of structure in the plates, showing the specific characters of each 

 form, and of an accurate diagnosis in their description, tends to increase the difficulty ; 

 any attempt, therefore, to clear up the synonymy of these species is hopeless, without an 

 attentive examination of the types themselves ; fortunately, this has been done by a most 

 competent and learned observer, M. Cotteau, whose analysis of the species will be given 

 when treating of the affinities of the urchin now under consideration. 



In my Memoir on the Cidaridse of the Oolites, I erroneously identified this species 

 with Pedina rotata, Agass., which is now considered by MM. Agassiz and Desor to be a 



