PECTEN. 



213 



dorsal area with four small radial ribs ; postero-dorsal area with four or five 

 (sometimes fewer) very small ribs. Ears very large and long, convex, with fine 

 concentric ridges; the anterior with a sinns ; the posterior larger than the anterior, 

 with the outer angle acute, and usually with six faint radial ribs. 



Left valve slightly concave or nearly flat, with a large apical angle ; length 

 greater than height, greatest length being above the middle line ; usually with 

 twenty-one rounded ribs of nearly equal size, separated by broader furrows, of 

 which six — corresponding in position with the main ribs of the right valve — are 



Fig. 3. Fig. 4. 



Figs. 3 and 4.— Pecten (Neithea) quadrico status, Sow. Upper Greensand, Warminster. Woodwardian Museum. 

 Natural size. Fig. 3, right valve ; Fig. 4, anterior view of the same. 



rather broader than the others. Antero- and postero-dorsal areas with small ribs. 

 Ears very large, elongate, triangular, with very small radial ribs. 

 Measurements : 



(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) 



Length . 74 67 67 66 63 52 78 71 56 58 57 36 71 58 49 33 mm. 

 Height . 77 70 68 66 65 52 75 67 56 58 57 36 66 51 41 30 „ 

 (1—12). Eight valves: 



(1 — 6) Upper Greensand, Warminster. 

 (7 — 9) Upper Greensand (zone of P. asper), Ventnor. 

 (10 — 12) „ ,, (zone of Schlcenb. rostrata), Blaekdown. 



(13_16). Left valves: 



(13 — 15) Upper Greensand (zone of Schlcenb. rostrata), Warminster. 

 (16) ,, ,, (zone of P. asper), Ventnor. 



Affinities. — This species resembles P. (Neithea) quinquecostatus, but is of larger 

 size, with usually only three ribs in each interspace, and with relatively larger ears 

 and longer hinge-line. 



A form found in the Senonian was described and figured by d'Orbigny ;is 



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