PECTEN. 191 



Ajjinifit'^. — Tliis species resembles P. asper (see p. 186), but is much smaller, 

 less couvex, with fewer folds (or maiu I'ibs), aud, iu specimens of the saiuc 

 size, with more numerous aud more closely placed ribs. 



When describing the Mollusca of the Chalk Rock (1807), I referred this species 

 to /'. ternatiis, Goldfuss, Avhich was founded on a cast from the Quader Sandstone 

 of Schandau (Saxony), and ajjpears to be the form usually known as P. Dujardini. 

 On farther examination this determination did not seem altogether satisfactory, 

 and I have recently, through the kindness of M. Raoul Fortin and M. A. de 

 Grossouvre, received specimens of P. Dujardini from France ; Professor Deicli- 

 miiller has also sent me casts of Geinitz' figured specimens. I am now able 

 to say that P. Dujardini differs from P. pexatus in having much stronger and more 

 distinctly separated folds, with less distinct ribs and spines, and in having closely- 

 placed concentric lamellae ; in specimens larger than those figured by d'Orbigny 

 the ventral margins of the valves are sharply bent. Two of the specimens figured 

 by Geinitz' (figs. 10, 11) may belong to P. pexatus, but they show the interior of 

 the valves only. I*. Dujardini appears to be more nearly related to P. septem- 

 pUcafns, Nilsson, than to F. pexatus. 



Distribution. — Zone of T. gracilis of Hooken (Devon). Zone of H. planus of 

 Cheveley (Newmarket). Chalk Rock of Winchester and Clothall (Baldock). 

 TJintacrlnus zone of Devizes Road (Salisbury). Zone of A. quadratus of East 

 Harnham. Zone of B. mucronata of Clai'endon (Salisbury), and of Shute-end Pit, 

 Alderburv. 



Pecten (^q,uipecten), sp. Plate XXXVI, figs. Ha,tK 



Description. — Shell small, flattened, ornamented with from ten to thirteen 

 narrow, elevated ril^s, which are separated by broad, flat interspaces. Ribs Avith 

 hollow, curving spines, placed at regular and fairly distant intervals. 



Beniarls. — This form, of Avhich I have seen three specimens oidy, appears to be 

 distinguished from P. asellus, Sowerby," by the spines on the ribs. It differs from 

 P. rarispimis, Reuss," in the absence of radial folds. 



Distribution. — Chalk Rock of AVinchester. A. quadratus zone of East Harnham 

 (Salisbury) and near Winchester. 



1 ' Das Elbthalgeb. in Sachsen' (1872), pt. 2, pi. x. figs. 10, 11. 



2 J. de C. Sowerby, in F. Dixon, ' Geol. Sussex' (1850), p. 348 (p. S83, ed. 2), pi. xxviii, fig. 5. 

 The locality and horizon of P. aselhis are not given by Dixon, and the type cannot now be found. I 

 have seen no example which could be referred to this species. 



3 'Die Verstein. der bohm. Kreideformat.' (1846), pt. 2, p. 31, pi. xxxix, fig. 15; Geiniiz. " Das 

 Elbthalgeb. in Sachsen" (' PaliBontographica,' 1872, vol. xx, jit. 2), p. 36, pi. x, fig. 13. 



