PECTEN. 19] 
Affinities.—This species resembles P. asper (see p. 186), but is much smaller, 
less convex, with fewer folds (or main ribs), and, in specimens of the same 
size, with more numerous and more closely placed ribs. 
When describing the Mollusca of the Chalk Rock (1897), I referred this species 
to P. ternatus, Goldfuss, which was founded on a cast from the Quader Sandstone 
of Schandau (Saxony), and appears to be the form usually known as 2. Dujardini. 
On further 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 Deich- 
miller has also sent me casts of Geinitz’ figured specimens. I am now able 
to say that P. Dujardini differs from P. pevatus in haying much stronger and more 
distinctly separated folds, with less distinct ribs and spines, and in having closely- 
placed concentric lamellz; 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. pevatus, but they show the interior of 
the valves only. P. Dujardini appears to be more nearly related to P. septem- 
plicatus, Nilsson, than to P. pevatus. 
Distribution.—Zone of T. gracilis of Hooken (Devon). Zone of H. planus of 
Cheveley (Newmarket). Chalk Rock of Winchester and Clothall (Baldock). 
Uintacrinus zone of Devizes Road (Salisbury). Zone of A. quadratus of Kast 
Harnham. Zone of 2. mucronata of Clarendon (Salisbury), and of Shute-end Pit, 
Alderbury. 
Prcren (ANQUIPECTEN), sp. Plate XXXVI, figs. 8 a,b. 
Description.—Shell small, flattened, ornamented with from ten to thirteen 
narrow, elevated ribs, which are separated by broad, flat interspaces. Ribs with 
hollow, curving spines, placed at regular and fairly distant intervals. 
Remarks.—This form, of which I have seen three specimens only, appears to be 
distinguished from P. asellus, Sowerby,’ by the spines on the ribs. It differs from 
P. rarispinus, Reuss,* in the absence of radial folds. 
Distribution —Chalk Rock of Winchester. A. quadratus zone of East Harnham 
(Salisbury) and near Winchester. 
1 «Das Elbthalgeb. in Sachsen’ (1872), pt. 2, pl. x, figs. 10, 11. 
* J. de C. Sowerby, in F. Dixon, ‘ Geol. Sussex’ (1850), p. 348 (p. 683, ed. 2), pl. xxviii, fig. 5. 
The locality and horizon of P. asellus 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, pl. xxxix, fig. 15; Geinitz, “ Das 
Elbthalgeb. in Sachsen” (‘ Palasontographica,’ 1872, vol, xx, pt. 2), p. 36, pl. x, fig. 13. 
