BY THE REV. J. E. TENISON-WOODS, F.G.S., F.L.S. 239 



It may be as well here to review all the described Australian 

 mesozoic species of Trigonia. They are T. costata, Clarke, which 

 is the same as T. morei, Lycett, T. lineata, Moore, T. ?iasuta, 

 Etheridge. 



The name T. costata, was applied by the Rev. W. B. Clarke, 

 F.R.S., to a species from Western Australia (Greenough River), 

 under the belief that it was Trigonia costata of Parkinson.* In 

 Moore's paper already referred to, the differences between the 

 species are pointed out by the late Mr. Lycett, and the Australian 

 one, named T. moorei. It is one of the group called Costatce, and 

 therefore entirely different from the new fossil described here. 



Trigonia lineata, Moore (loc. cit. p. 255) was described from two 

 imperfect specimens, one a cast showing the teeth, and the other 

 much abraded. It is a gibbous form, as broad as long, and there- 

 fore quite distinct from our species. Professor McCoy placed it 

 with the Permian and Rhsetic genus Myophoria, but Mr. Moore 

 considered that the absence of the oblique keel and the acute 

 posterior side, precluded such a reference 



Trigonia nasuta, Etheridge (Jour. Geol. Soc. Lond. 1872, p. 339, 

 pi. xix., figs. 2, 2a). This fossil was described from a cast only, 

 but which Mr. Etheridge says, belongs to a type unknown in 

 Jurassic rocks. It is much higher and deeper than our fossil, and 

 was referred to the group Scabrce nearest to T. sanctoz crucis, 

 Pictet and Camp., but a discovery of the external surface, might 

 show it to be much nearer to the present species. 



Pecten psila, sp. nov. P. t. parva, trigonali-orbiculari, wquivalva, 

 valde depressa, vix convexiuscula, omnino kevi, vel marginem versus 

 tenuissime concentrice striata, auribus incequalibus, radiatim costatis, 

 antice elongata triangulala producta, posteriore jiabelliformi. 



Shell small, suborbicular, equi valve, depressed, hardly convex, 

 entirely smooth, and without ornament of any kind, except one or 

 two very faint lines of growth near the exterior margin ; ears 



* Organic Remains, vol. 3, pi. 12, fig. 4 ; Paleontograph Soc. Monograph, 

 Lycett and Moore, Molmsca of the Great Oolite, pi. 5, fig- 23 ; Lycett. 

 Brit. Foss. Trigonia, vol. 33, p. 227, a wood cut of T. Moorei. 



