204 



PKOE. REYNOLDS AND MR. V AFGHAN ON THE [May I9O4. 



MODIOLA MINIMA, Sow. 



Our specimens agree well with Moore's large figure (1), pi. xv, 

 fig. 27. 



The anterior, upper slope (formed by the hinge-line) is somewhat 

 shorter than the posterior, and rises at an angle of about 20° ; the 

 posterior slope is nearly straight : the angle between the two 

 slopes is about 145 : . The greatest breadth occurs at the junction 

 of the two slopes, and is nearly half the largest dimension. The 

 lower border is nearly straight. The front end is pointed, but there 

 is no distinct separation of a lower, anterior, swollen portion. 



Specimens are not uncommon throughout the Rhaetic. 



Myophoria postera, Qu. ('2). 



Especially common at the maximum of Avicula contorta. 



Caedinia concinna, Sow. aff. re- Fig. 4. — Diagram of Cardinia 

 gularis, Terq. (PI. XVIII, concinna. Soiv. ((iff'. C. regu- 



lig. 4, & text- fig. 4.) laris, Terq. ). 



General contour uniformly 

 oval ; lower border broadly and 

 uniformly convex ; hinge-line 

 nearly straight, and only slightly / 1^ \v^_ 

 converging. Curvature of an- 

 terior and posterior borders 

 nearly equal. Beak not pro- 

 minent : lunule small. The 

 growth-lines form strong con- 

 centric bands. [Magnified 2 diameters.] 



Dimensions in millimetres. 



Spec. 1. Spec. 2. 



Horizontal " 21 30 



Vertical 13 16o 



Position of beak 5-16 7-23 



Radius of curvature of anterior border 5 5 



Radius of curvature of posterior border ."> 4'5 



As Brauns points out (5), p. 338, it is impossible to separate the 

 species of Cardinia on slight changes of form, between which there 

 is every possible mutation. He has consequently limited the number 

 of Lower Jurassic species to three, namely : C. concinna, C. crassi- 

 nscida, and C. Listeri. 



The separation of the elongate, regularly-oval concinna from the 

 tall triangular Listeri is a matter of the utmost simplicity ; but the 

 allocation of intermediate forms is extremely difficult, and is usually 

 almost valueless, as representing nothing more than the individual 

 weight attached to certain variable characters by a particular 

 author. For example, Brauns distinguishes C. crassiascida from 

 C. concinna by the following characters (op. cit. p. 340) : — 



