168 GASTEROPODA OF THE INFERIOR OOLITE. 



ornaments are similar to those on the whorls of the spine ; base finely striated ; 

 other indications wanting. 



Relations avid Distribution. — D'Orbigny relied upon the presence of the row of 

 fine spiral knots at the anterior margins in the type G. comma to separate it from 

 G. opis. If this be a valid difference, then our specimen should be called C. opis. 

 But I regard the difference as more a question of preservation than anything else. 

 This variety occurs in the upper part of the Eumphriesianus- zone at Sherborne, 

 where it is very scarce. 



94. Cbeithium comma, variety near to G. unitorquatum, Heb. and Desl. Plate X, 



fig. 3. 



The step-like character is fully maintained in this variety. The chief differ- 

 ences are in the ornamentation. The longitudinal costse are more nodular on the 

 upper margin of each whorl, and bifurcate much higher up. The closeness of the 

 tubercles gives the aspect of a narrow band on the upper margin of the whorls, 

 which answers to the " cordon transversal etroit " of Hebert and Deslongchamps 

 (' Foss. Montreuil-Bellay,' p. 41, plate vi, fig. 3). 



This variety occurs in the Parkins oni-zone of South Dorset — Bridport Harbour, 

 Burton Bradstock, Vitney Cross, and Loders, but it is somewhat rare, and 

 extremely difficult to extract in good condition. 



95. Cerithium circe, D'Orbigny, 1850. Plate X, fig. 4. 



1842. Melania scalabifoemis, Desl. (pars). Desl., vol. cit., pi. xi, fig. 66. 

 1850. Ceeithium ciece, B'Orb. Prod., vol. i, p. 271. 



Bibliography, fyc. — D'Orbigny's species is described as much elongated, and 

 the whorls, which are step-like, as costulated transversely by arched ribs. This is 

 the name applied usually in Calvados to the whole comma-group without any 

 distinction. They are much more plentiful there than with us. 



Description. — Length 32 mm., width 8*5 mm., spiral angle about 15°, and 

 regular; whorls slightly concave, and increasing by steps, though slightly. 

 The longitudinal ornament is conspicuous, consisting of close-set semilunar costse, 

 which extend entirely across the whorls. These are irregularly flexuous at times, 

 but as a rule do not bifurcate ; each terminates posteriorly in a tubercular 

 thickening, which adds to the tabulate character of the whorls. 



