138 CRETACEOUS LAMELLIBRANCHIA. 
lamella and well-marked growth-lines are present. The ribs vary in number 
considerably in different specimens, but are always more numerous near the ventral 
margin than near the umbo, owing to the imtercalation of new ribs. Left valve 
ornamented with similar but usually broader and more rounded ribs, crossed by 
numerous concentric lamellee. 
Measurements : 
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Length . . 53 48 47 39 36 38 31 30 25 22 22 17 mm. 
Height’ . . 48 44 46 51 40 38 28 36 28 30 29 20 
Number of ribs 
33 
at margin of 
right valve . 39 34 25 29 23 19 19 24 24 26 28 11 
(1—7, 11, 12) from the Gault of Folkestone ; (8—10) from the Gault near Cambridge. 
Affinities —See P. inflata (p. 140). 
Remarks.—This species was described by Sowerby as Plicatula pectinoides 
(Lamarck). The type of Lamarck’s species came from the Lias of Metz,? and is 
quite distinct from the Cretaceous species; the latter must, therefore, be known as 
P. gurgitis, Pictet and Roux. 
Types.—The types of P. pectinoides, Sowerby, from the Gault near Cambridge, 
appear to have been lost. 
Distribution—Gault of Folkestone (zones i—ili, vi, vill, x, xi), of Ford (near 
Aylesbury), and of Barnwell (Cambridge). Cambridge Greensand (derived from 
the Gault). Red Limestone of Hunstanton. Upper Greensand of the Isle of 
Wight. 
PricaTuLa minuta, Seeley, 1866. Plate XXV, figs. 22—25. 
1866. Puricatuta minuta, H. G. Seeley. Ann. Mag. Nat. Hist., ser. 3, vol. xvii, 
p. 176. 
Remarks.—The ornamentation of this small form is of the same type as that of 
P. gurgitis, but the ribs are perhaps more numerous than at the umbo of that 
species. Comparison, however, is difficult, since the umbo of P. gurgitis is seldom 
well preserved. It seems probable that P. minuta is only the young form of P. 
gurgitis, but since the smallest known example of the latter is very much larger 
1 Measured obliquely from the umbo to the middle of the ventral margin. 
2 Placuna pectinoides, Lamarck, ‘ Anim. sans Vert.,’ vol. vi (1819), p. 224. Plicatula pectinoides, 
Defrance, ‘Dict. Sciences nat.,’ vol. xli (1826), p. 400; Deshayes and Milne Edwards, Lamarck’s 
‘Anim. sans Vert.,’ ed. 2, vol. vii (1836), p. 178; d’Orbigny, ‘Prodr. de Pal.,’ vol. 1 (1849), p. 238. 
