ARTEMIS. 429 



markings, either disposed in linear zigzags (more rarely 

 clouded ones), or in numerous narrow rays (which are ge- 

 nerally rather interrupted), or in two or three hroad (and 

 usually continuous) ones. The irregularity of the concen- 

 tric striae, by which it is roughened, and the strongly 

 marked lines of increase give it a very coarse and subimbri- 

 cated appearance ; the closely set interstitial spaces look, 

 when magnified, like large and elevated striae. There is 

 no radiating sculpture whatsoever, nor are the strise-Iike 

 lines raised into lamellae at their extremities or elsewhere. 

 The ventral margin is moderately arcuated, and has a ten- 

 dency to rise rather the more anteriorward. The declina- 

 tion of the dorsal edges is remarkably trifling ; the front 

 one is extremely short, and, from the peculiarity of the 

 lunule, appears deeply incurved, although when examined 

 internally its outline is actually a little convex ; the hinder 

 one, which is very manifestly the higher margin, is at first 

 subrectilinear and scarcely sloping, increasing afterwards in 

 convexity and declivity, its termination, except in aged in- 

 dividuals, is usually above or on a i^ar with the level of that 

 of the anterior dorsal. Both upper corners are slightly 

 angulated, both lower ones are thoroughly rounded. The 

 posterior side is decidedly the broader ; its edge, as well as 

 that of the anterior extremity, is at its upper part rather 

 perpendicular and not greatly curved. The umbones are 

 not very prominent ; and the beaks, which are acute, dis- 

 tinct, and not coloured, turn very considerably forward ; in 

 front of them is a very deeply impressed heart-shaped 

 lunule, which is not abbreviated in shape, is almost in- 

 variably coloured, and whose lips are almost always more 

 or less pouting. The sunken ligament is almost entirely 

 concealed ; there is neither a flattening nor the slightest 

 excavation of the posterior dorsal surface. The interior is 



