The Invertebrate Fauna of the Uitcnhaye Series. 105 



the area above, a second row of less well-defined tubercles is situated 

 just below the longitudinal groove, while a third row of well-spaced 

 stronger tubercles limits the area below. Prominent transverse ridges 

 or irregular ribs cross the area in the posterior half of an adult 

 individual, terminating above and below in the marginal tubercles 

 and also between them. These ridges make their first appearance 

 somewhat abruptly, and become more strongly marked and also 

 more irregular in their form and spacing towards the posterior end 

 of the area, in a well-grown individual. A few may even pass over 

 to the flank and be there partly identified with ridges of growth. 

 The longitudinal groove of the area, which divides it into a 

 narrower, superior, and broader inferior portion, forms a constriction 

 in each transverse ridge. 



The escutcheon is narrow and relatively very elongated. It is 

 ornamented by irregular rows of coarse tubercles or prominent ridges 

 which pass very obliquely across its surface and terminate anteriorly 

 at the cardinal margin. They are seen to be frequently continuous 

 with the ornaments of the area. The ligament pit is of narrow and 

 elongated lanceolate form, and in a large individual extends to half 

 the length of the escutcheon. 



The central tooth of the left valve is very massive and prominent, 

 with relatively narrow apical angle. The anterior tooth of the right 

 valve is supported by a well-raised platform. At the posterior end 

 of the valves the raised ridge on the internal surface which separates 

 the siphonal channels is situated high up in the siphonal border 

 and is of relatively great strength and extent ; in a fully grown 

 individual it can be traced for at least 25 mm. from the margin. 

 Dimensions.- (1) (2) (3) (4) 



Length (about) 98 . 110 . 120 . 132mm. 



Greatest height 75 . 78 . 87 . 88 



Depth of a single valve 18 . 20 . 22 . 25 



Occurrence. Specimens in the collection of the South African 

 Museum came from the Sunday's Eiver (285 to 288, 290 to 296, 299). 

 Mr. Rogers collected this form on the left side of Coega Valley, half 

 a mile down from the railway (458g). An immature specimen from 

 Brentford, Knysna Estuary (150h), is also probably referable to 

 T. holubi. 



Remarks. The characters of this shell appear to be on the whole 

 very well defined, while the valves are especially conspicuous both 

 by their large dimensions and their salient ornamentation. Most of 

 the specimens submitted to me, in all of which the shell is replaced 

 by coarsely crystalline calcite, have had the surface considerably 



