470 FISSURELLID^. 



surfaces are rather flattish or even a little concave ; so too 

 is the anterior superficies, the hinder one is tolerably arched. 

 The shell is strong, opaque, and devoid of lustre. On a 

 ground of white, which is rarely pure, often is squalid, and 

 not unfrequently is tinged with green or ochre colour, from 

 about five to eight rather irregular rays, sometimes broken 

 into more or less confluent spots, may be observed : these 

 are dark grey, brownish grey, olivaceous or even dirty 

 green ; the colouring, in truth, is by no means brilliant. 

 The sculpture demands particular attention, since, unless 

 due regard be paid to its peculiarities, the species will 

 inevitably be confused with some of its many allied exotic 

 congeners. A reticulation is effected by the decussation oi 

 very numerous radiating costellae, and frequent concentric 

 elevated lines. The former are rather strongly elevated, 

 not much rounded, alternately slightly larger and smaller, 

 closely disposed (we have counted fifty upon a specimen 

 not an inch long), yet always with a distinct but very 

 narrow interstitial space ; the latter are much less coarse 

 and prominent, are moderately far apart, and become 

 somewhat lamellar, or even a little squamular (not nodose), 

 at the intersection.* The vertex is before the middle of 

 the shell, but is not marginal ; in the very young it is fine 

 and subspiral (at this stage the foramen precedes it), but 

 soon becomes worn off, and the summit is then occupied 

 by a rather small simple oblong perforation, of mIucIi the 

 internal ring or border is tolerably broad, not difl'erent in 

 colour from the general white hue of the interior, and is 

 sometimes rounded, but more often subtruncated, ante- 

 riorly. The basal margin is strongly dentated, and the 



* In Patella Grceca of Linnaeus, the ribs and concentric lines are much more 

 closely disposed ; in Fissurella Grceca of Lamarck, the clathration is much 

 coarser, and nodulous at the intersection. 



