90 FAUNA OF THE CORNBRASH. 



last volution is rounded ; the base has a few striations ; the columella is oblique ; 

 and the aperture somewhat triangular." From Scarborough. In the Sedgwick 

 Museum. 



Description. — This type shell being preserved, we can compare it with the 

 description and ascertain the exact meaning of the words, it being remembered that 

 at the time it was described the specimen was unique. Four costellas to a volution 

 means on the upper part ; the depressed striated band means that it is not raised 

 on both sides, leaving the upper portion of the base unconcealed. The base " has 

 a few striations," means apparently that they are not so strong or that they 

 diminish towards the columella, for the base is really characterised by the 

 abundance of striation. These are the spiral ones, which are very close on the 

 upper edge, are coarser after they run on to the actual base, and gradually get 

 more remote or weaker till the very edge of the columella. The upper edge is 

 crenulated at the top by the lines of growth, and all the " granulated costellas " 

 are about equal in size. The nearer the apex the more regular all become. The 

 anterior edge is rounded; in youth it is more so. 



Distribution. — This, or the next allied species, is now fairly common, there 

 being about twenty seen from Scarborough, and probably one or more from 

 Bedford, but they were not separated at first. 



Relations. — With regard to T. scarburgensis, it appears to be the younger 

 portion of the typical shell. Its spiral angle is said to be wider, but only by the 

 difference between 65° and 70°, which, on a comparison of several specimens, is quite 

 within the range of variation. It is said to be devoid of the basal belt, and this is 

 hard to distinguish in the upper whorls of all. For the differences between this 

 species and T. lacuna see that species. It is somewhat of a rough species when 

 full grown, but not the roughest. 



Trochus lacuna, sp. nov. Plate VIII, fig. 19. 



1885. Trochus strigosus, Hudlestou, Greol. Mag. [3], vol ii, pi. iii, fig. 4 (not the rest). 



Type (the same specimen as figured by Hudleston). — Length, apex restored, 

 35 mm. ; greatest breadth, 25 mm. ; whorls, about G. On the upper part of 

 each there are four spirals divided obliquely by lines of growth, the three anterior 

 of which are equal, but the most posterior rises to a greater height, and is separated 

 by a deeper interval; it abuts against the basal belt of the preceding whorl, and is 

 sometimes larger than it. The basal belt is separated from the upper part by a 

 deep spiral furrow, to which it forms the outer boundary, projecting beyond the 

 shell above. It is also separated on the basal side by a parallel depression facing 

 downwards. The band thus formed is flat externally, and is lineated spirally, and 



