Jurassic Mollusca from Arabia. 15 



eful (levelojjment it has been possible to almost coin- 

 expose the lateral area and a portion of the periphery 

 I. tigs. 1 a, h). In its crushed state the fossil has the 

 ng dimensions: — diameterof outer whorl 92 mm. (1) * ; 

 of outer whorl 30 (0*326) ; width of umbilicus about 

 1:2) ; the thickness of the whorl being indeterminable, 

 are 42 or 43 principal ribs in the outer whorl ; each, 

 raversing the narrow umbilical wall of the whorl, 

 forward in crossing the lateral area and bifurcates at 

 the middle of this area into two equally strong ribs, 

 cross the periphery without any interruption in an 

 Duvex curve. Occasionally, but very rarely, there is a 

 )al rib which does not bifurcate. There is no trace of 

 ture-line. 



i fossil is most probably referable to J. de C. Sowerby's 

 nites torquatus. The type-specimen, which came from 

 Desert N.E. of Cutch ■'•' f, has the following measure- 

 : — diameter of shell 64'5 mm.| (1); height of outer 

 21"5(0'33); thickness of outer whorl 23 (0'35), and 

 of umbilicus 28 (0-43). The outer whorl bears 41 

 5al ribs. Thus it will be seen that both in measure- 



and ornaments the Arabian shell approaches very 

 ^ the Cutch form. In his work on the Jurassic Cepha- 

 , of Cutch, Waagen § figures only a large completely 

 3 examjjle, and states that all the specimens in the 

 im of the Geological Survey of India came from " the 

 red iron-sandstone of the Katrol range, that is, from 

 .ddle region of the Katrol Group." It is stated to be 



the commonest Ammonites of the Katrol Group 'i. 

 rnaments of the Arabian fossil agree very closely with 

 of the larger of the two specimens (figs. 6, 6 a) from 

 »iti Valley figured by H. F. Blanford ^, and referred by 

 vith a query to Sowerby's species. Unfortunately 

 r the suture-line nor the form of the transverse section 

 .liable for comparison in the Arabian fossil. The 



e numbers in parentheses accompanying the dimensions measiu-ed 



^metres indicate the proportion of each of them to the whole 



;r taken as unity. 



. cit. p. 719. The specimen is now in the Museum of the Geolo- 



)ciety of London. 



e specimen is 68 mm. in diameter, but owing to the imperleclion 



nterior end its dimensions can be best taken at a diameter of 



n. 



. Waagen, op. cit. pt. 2, 187o, p. 101, pi. liv. 



D. Oldham, Manual Geol. India, 1893, p. 222. 



F. Blanford, Journ. Asiat. Soc. Bengal, vol. xxxii. 18G3, p. 130, 



gs. 6, 6 a, 7, 7 a, 8. 



