6 Frederick Chapman: 



Observations. — The long, triangular shape of the shell reminds- 

 one of P. australis, Lamarck.s of the Philippines, but does not show 

 the dominant sharp median ribs of that species, which extend from 

 umbo to margin. 



Occurrence. — In the Lower beds at Muddy Creek, near Hamilton,. 

 Victoria. Of Balcombian (Oligocene) age. Found by the late Mr. J. 

 H. Young. 



Plicatula dennanti, sp. nov. (Plate I., Figs. 6, 7.) 



Description. — Shell roundly trigonal, distinctly oblique. Right 

 valve depressed, with more or less inflated umbo and marginal area; 

 left valve depressed. Plicae few, about 7, bifurcating and rather 

 acutely ridged. Teeth situated on a small, triangular hinge-plate. 



Dimensions. — Right valve (cotype) ; height, 22 mm.; length, 18.5 

 mm. Left valve (cotype); height, 19 mm.; length, 15.5 mm. 



Observations. — There are three examples of this species in the 

 Dennant collection at the National Museum — two right valves and one 

 left. A note by the late Mr. Dennant which accompanies this form 

 says, " allied to P. essingtoncnsis.'" That species, however, differs from 

 P. dennanti in the more numerous plicae, which are quite sharp; and 

 in the nearly equilateral form of the shell. P. essingtonensis,. 

 Sowerby,9 is a Northern Australian shell. 



Occurrence. — Lower beds at Muddy Creek, near Hamilton. Dennant 

 collection. Of Balcombian (Oligocene) age. 



Plicatula brevispina, sp. nov. (Plate I., Fig. 8.) 



Description. — Shell subtriangular, moderately stout, slightly 

 oblique. With about eighteen plicae, rarely bifurcated, slightly ridged 

 and crossed by undulating growth-lines, which develop into nodose 

 spines at their intersection near the ventral margin. The attached 

 umbonal area flat, from which the shell slopes away at a steep angle. 

 Teeth attached to a short dental plate, which is obliquely striated. 



Dimensions. — Height of right valve, 25 mm. Length, 22.5 mm.- 

 Depth of valve, 7 mm. 



Observations. — This species differs from P. youngi in the rounder 

 outline, the sharp nodose ribs, and the smaller dental plate. 



It is a very ornate form compared with other species, and the 

 fossil example is well preserved. In the style of ornament it is not 

 unlike P. novae-zelandiae.^o but that species is more depressed. 



Occurrence. — Lower beds Muddy Creek, near Hamilton. Of Bal- 

 combian (Oligocene) age. Dennant Collection. 



8. Anim. sans Vert., vol. vi., p. 85. Reeve, Conch. Icon., vol. xix., 1873, 

 pi. iii., figa. 10a, c, d. 



Reeve, Conch. laon., vol. xix., 1873, pi. iii., fig. 8. 



10. Sowerby in Reeve, Conch. Icon., vol. xix., 1873, pi. i, fig. 1. 



