Jurassic Molluscafrom Arahia. 7 



resemblance to ^rca (CucuUcea?) Jonesi of Tate* from the 

 Uitenhage beds of South Africa.' 



Like the Indian and African specimens, the Arabian 

 examples are sometimes a good deal crushed, although two of 

 the largest left valves exhibit their natural convexity. The 

 valves also vary in size, the largest having a height of 30 mm. 

 and a length of 54 ram. 



The ligament area in most examples is not preserved, but 

 a sectioned left valve shows a fairly deep concavity beneath 

 the umbo, but unfortunately without surface structure ; this 

 same specimen exhibits evidence of the elongate horizontal 

 teeth at the posterior end of hinge-line, which serve to indicate 

 the generic position of this species. 



Loc. Near Dihala. 



Genus NUCULA, Lamarck. 



Nucula cuneiformis , J. de C. Sowerby. 

 (Pi. I. figs. 5-7.) 



Modiola, J. D. Herbert, Gleanings in Science, 1831, vol. iii. pi. xvii. 



fig. 5, p. 272 ; Everest, Asiatic Researches, 1833, vol. xviii. pt. 2, 



fig. 28, p. 114. 

 Nucula, J. de C. Sowerby, Asiatic Researches, 1833, vol. xviii. pt. 2, 



p. 278. 

 Nucula? cuneiformis, J. de C. Sowerby, Trans. Geol. Soc. London, 



1840, ser. 2, vol. v. pi. xxii. fig. 4, p. 328. 

 Nucula cuneiformis, II. F. Blanford, Jouru. Asiatic Soc. Bengal, 1863, 



vol. xxxii. p. 135. 

 Nucula cuneifor^nis, Stoliczka, Mem. Geol. Surv. India, 18G5, vol. v. 



p. 90. 



Among the Arabian specimens are some inflated examples 

 of a Nucula which show so great a resemblance to N. cunei- 

 formis from the Jurassic rocks of Spiti and Catch that I am 

 unable to separate them from that species. 



Li Sowerby's original description of the shell it is stated 

 to be " transversely elongate-elliptical, gibbose, smooth ; 

 beaks f close to the anterior extremity, small, incurved." 



Unfortunately the type of the species is missing from 

 Capt. 0. W. Grant's collection of Cutch fossils in the Geolo- 

 gical Society^s Museum, although I am enabled to institute 

 a comparison, as there happens to be an example of this shell 

 (determined by myself) in the Rev. J. F. Blake^s collection 



* Quart. Journ. Geol. Soc. 18137, vol. xxiii. pi. ix. fig. 9, p. 101. 



t It may be here mentioned that Nucula is one of the few genera 

 which has posteriorly directed umbones (opisthogyrous) ; therefore the 

 position of the '* beaks " should be referred to as posterior, and not 

 anterior. 



