88 FAUNA OF THE CORNBRASH. 



Family Trochidje. 

 Genus TROCHTJS, Linnaeus. 



Whatever may be the extreme limits of this genus, the species here included 

 have all short spires, conical surfaces, angular base margins, and ornaments above 

 that limit different from those below. 



The records of Trochus are : 



* T. bunburyi. * T. strigosus (34, 43, 48). 



* T. monilitectus (6, 28, 43, 48). * T. subglaber (48). 



* T. scarburgensis (48). 



T. bunburyi is not represented by any specimen, nor can I obtain any 

 information as to whence the specimen quoted came. T. monilitectus is the 

 general name for the group to which the shell belongs. It is here described 

 under the name T. duplicans. T. scarburgensis is here included with T. strigosus. 

 for which see p. 89. For T. subglaber see p. 89. 



Trochus duplicans, sp. nov. Plate VIII, figs. 15, 16. 



1885. Trochus monilitectus, var. B., Hudlestou, Geol. Mag. [3], vol. ii, p. 122. 



Type. — Length, 8 mm. Spiral angle 55° on slope, spire flat. Whorls 7. 

 The ornaments commence on the fourth, except the duplicated spiral, which 

 commences on the third. In the adult the most anterior spiral projects more, but 

 is no thicker than the rest. It is followed behind by three others like it, but the most 

 posterior spiral is duplicate, being divided by a spiral furrow into pairs of knobs 

 by dividing lines which go in the forward direction away from the aperture. In 

 the larger interspaces finer spirals may be seen, while the coarser spirals are 

 divided into knobs by oblique lines, which are continued over the edge in the 

 same plane (and, therefore, apparently in a reversed direction) as radials. The 

 base is marked with twenty fine spiral lines right up to the columella. The inner 

 lip of the aperture clothes the previous whorl with a nacreous layer, the outer 

 lip itself showing two distinguishable layers. From Scarborough. In the 

 Sedgwick Museum. 



Description. — Although only one specimen answers exactly to the above 

 description, there is another which corresponds in all respects but one, that one 

 being the number of the threads. Instead of there being four and a double one 

 with a few finer interspersed occasionally, there are seven nearly uniform threads 

 in the same space, so that they nearly fill it. They are all crossed by lines like 



