30 EXDODONTID^I. 



the palatal folds as they appear from below the shell-wall; all the 

 figures are enlarged.) Two specimens in my collection measuring, 

 major diameter 6 millimetres, minor diameter 5*5, axis 3 milli- 

 metres have the anterior portion of the first series consisting of 

 four horizontal denticles, the first two close together, the third a 

 little smaller and further distant, and the fourth still smaller and 

 still further distant ; the anterior portion of the second series 

 possesses, in addition to the oblique curved denticle, a slight, 

 straight, horizontal denticle. Another specimen, also in my 

 collection, measuring 5*5 millimetres in diameter, has three hori- 

 zontal denticles in the first series, while the second series is similar 

 to that in my other two specimens. It possesses, however, in 

 addition, one posterior and two anterior denticles of a previous 

 set, separated from the mature set by a distance of 1 millimetre. 



Var. compressa, Sykes. 



Plectopylis (St/kesia) clathratula, var. compressa, Sykes, Proc. Make. 

 Soc. London, iii, 1898, p. 72, pi. 5, figs. 13, 14 ; Gude, Science 

 Gossip, N. s. vi, 1899, p. 75, fig. 101. 



Differs from the type in being more elevated, in the more con- 

 vex spire and the narrower umbilicus, while the raised ribs are 

 scarcely visible. The armature is similar to that of the type. 



Fig. 8. Riithvenia clathratula var. c&mprcsta. 



The specimen figured is in Mr. Ponsonby's collection : it measures 

 5 millimetres in diameter, altitude 2'5 millimetres. 

 Hob. Ceylon : Ambagamuwa (Collett). 



47. Ruthvenia caliginosa, Sylces. 



Original description : " Testa mediocriter umbilicata, lenti- 

 eularis, acute carinata, superne costulis obscuris remotis ornata, 

 parum uitens, corneo-brunnea, apice maguo, obtuso ; sutura bene 

 impressa; anfr. 5, plano-convexi, lente accrescentes, ultimus basi 

 inflatus, radiato-striatus ; apertura verticalis, angusta, angulato- 

 lunaris ; peristoma simplex, acutum ; plicae et dentes sicut (?) in 

 P. clathratula^ sed dentes palatales pauci. 



"Alt. 2-9, diam. 6 mm." (Sykes.) 



Hob. Ceylon : Ambagamuwa (0. Collett). 



" Shell slightly more elevated than P. clatJiratula, whorls a little 

 flatter, base more inflated, the umbilicus being little more than 



