126 CRETACEOUS LAMELLIBRANCHIA. 
sometimes less inflation than the left; the attached part bears concentric 
toothed lamella; the free surface has numerous regular, nearly equal radial ribs, 
separated by narrow grooves; in some cases the ribs carry short spines placed 
rather irregularly, and sometimes slender transverse ribs are seen. 
Left valve usually regularly convex, with numerous slightly unequal ribs, which 
are occasionally a little wavy. The ribs are separated by grooves, generally of 
greater, but sometimes of the same width. The spines on the ribs are hollow, 
usually short, sometimes perpendicular to the surface, sometimes sloping ventrally ; 
they may be developed rather irregularly, or larger spmes may be borne on slightly 
stronger ribs at regular intervals; between these ribs are three or two slightly 
smaller ribs, with sometimes smaller spines. Faintly marked transverse ribs occur 
in the grooves, and sometimes extend on to the ribs. Kars smooth, except for 
erowth-lnes. 
Measurements of left valve : 
(1) (2) (3) (4) (5) (6) (7) (8) (9) 
Length . 20 22°5 23 28 26 17 22 27 24 mm. 
Height . 23 25 250 26:0 30) 19: 5a 20 BONE, 
(1—5) zone of A. quadratus, East Harnham. 
(6—8) 39 x West Harnham. 
(9) Chalk of Trimingham. 
Affinities. —S. Omalii, d’Avchiac,’ appears to be a more oblique form with 
fewer ribs. The form referred by d’Orbigny”® to S. hystri# is larger than 
S. Dutempleanus, and has the spines confined to the neighbourhood of the umbo. 
Specimens from the Cenomanian of Devon and Orbiquet (Normandy) agree with 
the Turonian and Senonian examples, except that the ribs are a little more widely 
separated. Similar Cenomanian forms from St. Fargeau (Yonne) and St. Sauveur 
(Yonne) have also been referred to S. Dutempleanus by @Orbigny and by Peron. 
S. fimbriatus, Goldfuss,’ is very similar to S. Dutempleanus ; jadgmg from the 
fivures alone, the only difference appears to be in the fewer spies on the 
ribs. 
A specimen, described and figured by Sowerby * as Lima? spinosa, is perhaps 
an example of S. Dutempleanus. I have not been able to find the original, and the 
locality is not stated. 
Remarks.—In the majority of specimens seen the spines have been more or less 
completely broken in the process of clearing away the matrix. Examples from 
1 «Mem. Soe. géol. de France,’ vol. ii (1847), p. 312, pl. xv, fig. 11. 
‘Pal. Franc. Terr. Crét.,’ vol. iii (1847), pl. ecccliv, figs. 1—9. 
3 « Petref. Germ.,’ vol. ii (1836), p. 97, pl. evi, fig. 2. A specimen was referred to this species by 
Dixon (‘ Geol. Sussex,’ p. 356, pl. xxviu, fig. 34). 
+ F. Dixon, ‘ Geol. Sussex’ (1850), p. 347, pl. xxviii, fig. 33; p. 382 of ed. 2. 
1 
