Jurassic Mollusca from Arabia. 9 



concave on tlie upper surface, the last having a sharply 

 carinated periphery; base inflated and doubtfully umbilicate ; 

 aperture apparently subcircular ; sculpture comprising fine, 

 closely arranged, regular spiral striations both on the upper 

 and basal surfaces, crossed by oblique lines of growth which 

 are strongest and most evident at the base ; lower margin of 

 whorls obscurely tubercled. 



Dimensions. — Height = 22, diameter = 18 mm. 



The two specimens now described somewhat resemble the 

 genus Amberleya, though not so prominently turreted as 

 most known forms of that genus, and of much less decorative 

 sculpture than usually obtains. I know of no form of 

 Jurassic Trochidse similarly ornamented. About twelve of 

 the regular spiral lines can be counted on the surface of the 

 penultimate and body-whorl (where they are best seen), and 

 there are slight indications of tubercles on the periphery, 

 although the specimens are somewhat worn and coated in 

 places with the light-coloured matrix. 



The base is fairly ventricose, but whether there is an 

 umbilication or not is very uncertain, as the hard limestone 

 covers up this part o£ the basal region. 



The form is of interest to record as it accompanies the 

 shells found in the light-coloured limestone, and unques- 

 tionably forms part of the same fauna, although its relation- 

 ship to other species has not been traced. There is, however, 

 a slight similarity of structure to a form figured by Dr. Dacque 

 {Trochus sp. indet.) from the Kimeridgian of Somaliland 

 (Atschabo), but without specimens for actual examination a 

 more accurate comparison is not possible (pi. xvi. fig. 8, 

 p. 142 of Dacque's memoir, quoted in the list of literature), 

 although a peripheral keel is present on the lower whorl. 



Loc. Near Dihala. 



Genus Nerin^A, Defrance. 

 Nerin&a cf. desvoidyi, Orbigny. (PI. I. fig. 10.) 



Nerinaa desvoidyi, Orbigny, Prodrome Pale"ontologie Stratigraphique 



1850, vol. ii. p. 4 ; Pal. Francaise, Terr. Jurassiques, Gaste"ropodes' 



1850, pi. cclxi. p. 107. 

 Nerinaa gosce, Contejean, Kirnrne'ridien de Montb6liard, 1859, pi. vii. 



fio:. 1, p. 231 ; (pars) Thurman and Etallon, Letheea Bruntrutaua, 



1864, pi. vii. fig. 38, p. 93, non Ronier. 

 Nerincea desvoidyi, P. de Loriol, Mori. Paleont. Ge"ol. £tages Sup. 



Jurassique, M6m. Soc. Lina. Normandie, 1872, vol. xv. pi. vi. 



figs. 2-5, p. 81 ; Blake and Hudleston, Quart. Journ. Geol. Soc. 



1877, vol. xxxiii. p. 266. 



This specimen is a natural cast of a large fragment of 



