SPINIGERA. 107 



the wing and in communication with the channelled digitations. Canal long and 

 straight, but no complete termination has been seen. 



Varieties and Dimensions. — In the longer varieties, which constitute a consider- 

 able majority, the degree of compression, or ratio of minor to major axes of width, 

 which might be called the index of compression, is as 57 to 100. In the shorter 

 and wider varieties it is about as 50 to 100, i. e. one side of the shell is twice as 

 wide as the other. From 15 to 20 mm. in length seems to be about an average 

 for the narrower varieties. The large specimen (fig. 6 a) measures upwards of 

 30 mm., but this must be regarded as a megalomorph. The length in this case is 

 gained not by an additional number of whorls, but by the greater height of each. 



In the wide variety (fig. 6 d, and enlargements) the apical whorls resolve 

 themselves into an almost undistinguishable nucleus, the two costated whorls are 

 in their place, and the remainder of the shell appears in all cases to consist of four 

 instead of five whorls. Hence this variety seems to have arrived at maturity 

 earlier. The length of this variety may be taken at from 12 to 13 mm. 



Relations and Distribution. — This curious species helps to show the analogy which 

 exists between Maria and Spinigera. Unless we are prepared to believe that Sp. 

 trinitatis is a young or undeveloped form of Sp. didactyla, the latter stands almost 

 alone. If Spinigera trinitatis be an undeveloped form, then the two species, though 

 related, might be regarded as distinct. But if Sp. trinitatis be merely the young 

 stage of the other, then it is clear that they only form one species. The point is a 

 difficult one and not easy to decide. There is a considerable degree of resemblance 

 in the more apical portions of the spire. On the whole the anterior whorls, which 

 make up the bulk of the shell, are less angular in Sp. trinitatis, and show more 

 spiral ornamentation. 



Both forms are mainly confined to the Sowerbyi-bed at Bradford Abbas, and in 

 my own collection Sp. didactyla is the most numerous. These species are appa- 

 rently not known to occur in the Inferior Oolite of Normandy. 



26. Spinigera crassa, sp. nov. Plate III, fig. 7. 



Description . 



Length about . . . .25 mm. 



Shell subelongate, fusiform. Apex unknown. Whorls stout and subangular 

 (seven remain), with a strong keel placed towards the anterior extremity. No 

 spiral ornament visible, but the whorls are rugose with axial lines, most pro- 

 bably of growth. The bilateral varices in the only available specimen are not well 

 seen, and the spines are more or less broken off. Body-whorl sub-bicarinate, 



