136 



sculpture of the posterior area consists of concentric, raised striae or fine 

 ribs, which follow the curved outline of the shell, and in doing so bend 

 downwards, and again a little upwards at an obtuse or somewhat rounded 

 angle in crossing the farthest of the two grooves from the central space. 

 In some specimens the raised striai on the posterior area are much wider 

 than the spaces between them, and the surface of these may fairly he 

 called ribbed, but even in those individuals which are most finely striated 

 the striae on the posterior area are always perceptibly coarser and 

 farther apart than they are on any other part of the shell. 



BmTOWS cylindrical, lined with a calcareous tube, which is variously 

 bent or curved when the shell is immature, but which becomes nearl}^ 

 straight when the animal has attained its full size. The surface of the 

 posterior end of the tube, also, is marked by rather faint, but broad, 

 swellings, which alternate with obscure, narrow constrictions at irregular 

 intervals, and its closed termination anteriorly is subtruncated, with the 

 edges slightly bevelled off. 



South-west side of Denman Island, in Division B; J. Eichardson, 1872. 

 Sucia Islands, in Division A ; J. Eichardson, 1874. Tubes also, which 

 may belong to this species, were found at the east end of Denman Island, 

 in Division C, but no shells have been found in them, and the specimens 

 may have been derived from the underlying shales of Division B. 



An interesting and very curious species, of which only seven detached 

 valves have been obtained, none of which are quite perfect. In some 

 respects T. Sucitnsis comes very near to T. partita, T. crassula and T. 

 torulosa of Stoliczlca,* from the Cretaceous rocks of Southern India, but at 

 present it cannot be satisfactorily identified with either. The delicate 

 sui'face markings of the valves of T. partita and T. torulosa appear to 

 differ from those of T. Suciensis in more than one particular. Thus the 

 central area of T. partita is separated from the posteiior side by a single 

 deep gi'oove, and the striations of its whole surface are described as 

 being "extremely fine, so much so that they are often barely traceable." 

 As already pointed out, there are two faint, shallow grooves with an 

 obscure ridge between them on the anterior boundary of the posterior 

 area in T. Suciensis, and in that species the striations or fine ribs on the 

 same area arc very strongly marked. In T. torulosa there is stated to 

 be a single wide groove between the central and posterior areas, and its 

 central area is described as being wide, whereas it is very narrow in 

 T. Suciensis. So far as the sculpture alone is concerned, there are several 



• Cretaceous Pelecypoda of SouUiera, India, pp. 15 and 16, pi, l, flgs l, 2, and 3. 



