408 CHITONID^. 



between this species and the traditional marginatus, as well 

 as the circumstance (proved by the Linnsean cabinet) that 

 this was not the shell originally described as C. cinereus, we 

 have retained the name attributed to the species by Mr. 

 Lowe, who first clearly defined it, although the asellus of 

 Chemnitz is nearly as obscurely indicated as the cinereus 

 of Linnseus. 



The shape of this Chiton ranges from oval to ovate 

 elliptic, and the height from rather depressed to decidedly 

 elevated: in the latter case the dorsal ridge, which typically 

 is very obtusely subangular, is much more sharply angu- 

 lated. The plates, which are short in proportion to their 

 width, have their posterior curvature almost uninterrupted 

 by any central rostration, the summit of the valves not dif- 

 fering from the general surface in either colour, sculpture, 

 or elevation of area. The valves, towards their bases, are 

 concentrically grooved with rather profound sulci of in- 

 crease, and are divided into lateral and central triangles 

 rather by the style and disposition of the shagreening than 

 by any superior tumidity or line of demarcation on either. 

 The raised granules upon the central areas are arranged in 

 very numerous longitudinal moniliform or beaded series, 

 which are for the most part nearer to each other on the 

 more elevated portion of the valves than at the sides ; the 

 granules upon the lateral triangles, as well as those of the 

 anterior plate, have a somewhat radiating disposition, 

 are very close-set, and become coarser and less regular 

 towards the ligament. This last is roughly arenaceous 

 and narrow, the margin on each side taken together rarely 

 exceeding, even if it equal, one quarter the breadth of 

 the plates. 



The general colouring is sallow, fulvous, or cinereous, 

 often mottled or irregularly speckled upon the ligament 



