Trochus.] GASTROPODA. 107 



The fossil forms appear in the Secondary formation, and have a 

 wide distribution in the Tertiary. 



Vernacular Name. Top-shell. 



Remark. The genus is Indo-Australian, and not represented in 

 the Tertiary of Patagonia. (Von Ihering.) 



Subgen. 1. INFUNDIBULUM, Montfort, 1810. 



InfundHmlum, Mft., Conch. Syst., 167. Type : Trochus concavus, Gmel. 

 Infundibulum, Mft., Man. Conch. (1), xi, 7, 24. Polydonta, Schumacher, 

 Essai d'un nouv. Syst., 1817, 231 ; Ad., G.R.M., i, 414, not of Fischer 

 de Waldheim, 1807. Carinidea, Swainson, Treatise on Malac., 1840, 350. 

 Lamprostoma, Swains., i.e., 350. 



Shell conical, false-umbilicate ; columella more or less folded 

 above, its edge straight, oblique, toothed or simple, with or without 

 a tooth at the base. 



Indo-Pacinc and Australasian province. 



Sect. 1. CCELOTKOCHUS, P. Fischer, 1880. 

 Ccelotrochus, P. Fischer, Coq. Viv., 417. Type : Trochus tiaratus, Q. & G. 



The false umbilicus very deep and narrow, penetrating deeper than 

 the columella, which is inserted upon its edge, not in the centre of the 

 axis. 



KEY TO SPECIES. 



A. False umbilicus wide and very deep ; 5 to 8 beaded spiral 



cords on the penultimate whorl . . . . . . tiaratus. 



E. False umbilicus narrow and not very deep. 



a. Last whorl with a distinct peripheric keel . . . . chathamensis. 



b. Last whorl biang\ilate . . . . . . . . oppressiis. 



1. Trochus chathamensis, Hutton, 1873. Plate 33, fig. 2. 



Polydonta chathamensis, Hutt., C.M.M., 36. Trochus chathamensis, Hutt., 

 Man. Conch. (1), xi, 43 ; Suter, P. Mai. S., ii, 260, fig. in text. Anthora 

 chathamensis, Hutton, M.N.Z.M., 94. 



Shell small, conical, spirally striated, last whorl keeled, false 

 umbilicus shallow. Sculpture consists of 5 to 6 low spiral threads, 

 the lower and upper margins much elevated, especially the former ; 

 crossed by broad nodulous radiate ribs, which, however, do not extend 

 over the lower half of the whorl ; these ribs are often obsolete ; base 

 with subequal spiral lirse. Colour white, buff, or pinkish, with oblique 

 longitudinal brownish - purple stripes and spots. Spire conical, the 

 sides straight or slightly convex. Protoconch regularly conical, pointed, 

 of about 2 whorls, not marked off from the succeeding whorl, smooth, 

 with 2 or 3 spiral red bands. Whorls 5, rarely 6, the last 2 rapidly 

 increasing, flat to slightly convex above, concave below before reach- 

 ing the strong and prominent cingulum ; last whorl strongly carinated ; 



