SPATHELLA. 115 



which perhaps would render the margin a little concave if it were better displayed. 

 In this point it reminds one of the genera Modiola and Cypricardinia. 



Comparing it with the M. amygdalina of Phillips, it seems to me to agree 

 remarkably with his description, and on placing it in the oblique positions in which 

 his shell seems to be drawn, it assumes exactly the same form as his figure ; in 

 fact the shape of his drawings can only be explained by an anterior contour such 

 as exists in our shell. 



It is true that his figure shows much stronger growth-lines, but there is 

 some evidence of this in our shell, considering that it is in the nature of a cast. 



Affinities. Avicula pusilla, Barrande, 1 a much smaller and extremely variable 

 shell, occasionally approaches it in shape. 



2. Genus SPATHELLA, Hall, 1885. 



" Shell equivalve, very inequilateral, wider behind ; anterior end short, 

 narrowly rounded ; beaks subanterior, small ; umbonal slope rounded or sub- 

 angular ; surface with concentric striae, sometimes lamellose ; probably related to 

 the Lithophagi" 



The above are the characters given by Hall ; and if, as seems from them and 

 his figures, the following species belongs to it, it may be added that there seems 

 to be an external ligament, a large oval muscle-scar situated in the centre of 

 the anterior end, and a larger circular posterior muscle-scar situated on the upper 

 part of the shell near the posterior end. Along the posterior hinge-line the 

 surface seems concave, bearing two linear transverse ridges, but it does not 

 appear whether they form part of the hinge. 



1. SPATHELLA MUNDA, n. sp. Plate IX, figs. 1, 1 a ; and Plate XI, figs. 1, 2. 



Description. Shell moderate in size, convex, very oblique and transverse. 

 Hinge-margin very slightly curved, considerably less than the length of the shell, 

 bearing one or two long, linear, horizontal ridges, which seem to bend beneath the 

 umbo with hardly any break. Anterior margin very narrow and doubly convex, 

 almost subangular in front. Inferior margin very long, oblique and nearly 

 straight. Posterior margin very broad, semicircular below, becoming straight 

 and oblique above as it merges into the hinge-margin. Umbo low, wide, 

 flattened, proximate, slightly elevated above the hinge-line, tending forward and 



1 1881, Barrande, ' Syst. Sil. Bohetne,' vol. vi, pi. ccv, figs. 122, t. F, GK 



