LITTORINA. 41 



times nearly half again as broad as it is long; it is well 

 rounded, though a little flattened in the middle, and its 

 basal declination is, for the most part, low down, and rather 

 sudden. The mouth, which occupies rather more than 

 one half the length in the shorter specimens, rather less 

 than that proportion in the produced ones, has an ovate 

 contour, and is not contracted posteriorly ; its colour, if 

 not that of the exterior, is chocolate brown. The outer 

 lip is never thickened, is moderately arcuated, and is 

 united to the body at almost a right angle. The pillar lip, 

 which sometimes twists a little to the left, shelves inwards 

 and is somewhat dilated at the base of the shell ; its 

 inner or attached edge is arcuated and a little raised. A 

 large specimen of nearly eight lines in length, measured 

 six lines in breadth ; another produced and smaller sized 

 example, five lines long, only measured a quarter of an 

 inch across. 



Strange to relate, although the typical forms of rudis, 

 tenebrosa, patula, and saxatUis, are so very unlike, certain 

 aberrant individuals almost indicate, that they form but one 

 species. We have figured some specimens (pi. Ixxxiii. fig. 4, 

 and pi. Ixxxv. fig. 3, 4) that almost connect the first three 

 forms, but the greater production of the spire, the propor- 

 tional and slovt'er increase of the turns, and the possession of 

 an additional volution, induce us to refer them to the pre- 

 sent heading.* These shells, and certain allied forms, 



* The untigured L. ventricosa of Brown's Illustrations (p. 16), is probably one 

 of these links between tenebrosa and patula. We have not, however, observed 

 any specimens that precisely correspond to it. We transcribe the description of 

 its characters from the vvork alluded to : — ■" Shell rather thin, smooth, conic, 

 ventricose, body large, and the spire small, measuring only one-third of the length 

 of the body, consisting of four inflated, deeply separated volutions, and terminating 

 in a rather obtuse apex ; the superior part of the bodj', and volutions of the spire 

 somewhat flattened above, giving them a subcarinated appearance ; aperture sub- 

 nitund, dark burnt umber brown within ; outer lip thin, slightly inflected, and of 



