170 



Dimensions. — Antero-posterior diameter, 21 ; umbo-ventral 

 diameter, 12 ; sectional diameter of closed valves, 7 millimetres. 



Localities. — Clays at Schnapper Point, Port Phillip ; lower 

 beds at Muddy Creek; calciferous sandstone of the Eiver 

 Murray Cliffs near Morgan. 



Professor McCoy, in Eeport G-eol. Surv., Victoria, No. 2 y 

 figures on p. 22, under the name of Tellina Krausei, the im- 

 pression of a Tellina-like shell obtained near Stawell, and 

 states that the species is common in the Tertiary beds at 

 Schnapper Point. It may possibly be Semele Krauseana, with 

 which it agrees in shape, but doubtfully so, as the drawing 

 indicates an ornamentation of thick concentric ridges, unless, 

 however, it be faulty in this particular. The figure is unac- 

 companied by description. 



The species-name is in compliment to Mr. P. M. Krause, 

 P.G.S., Lecturer on Geology at the Ballarat School of Mines, 

 and late of the Geological Survey of Victoria. 



FAMILY MACTRID.E. 

 Genus Mactra. 

 synopsis of the species. 

 Broadly ovately-trigonal ; subacuminately produced pos- 

 teriorly ; wavy wrinkled at the sides. M. axiniformis. 

 Shorter and broader ; posterior side straight ; concentric 

 striae simple at the sides. M. Hamiltonensis. 

 Elongate-ovate, attenuated at the extremities. 



M. HowcMniana. 



Mactra axiniformis, spec. nov. Plate xvii., figs, la— 16. 



Ovately trigonal; thickish, rather tumid, inequilateral, 

 bluntly rounded in front, the posterior side the longer and 

 sub-acuminately produced. Ventral margin broadly arched, in- 

 conspicuously insinuated towards the posterior extremity ; 

 dorsal margins about equally sloping, the front a little arched, 

 the posterior one longer, at first slightly ecurved, thence 

 straight. The surface is shining, brown with zones of lighter 

 colour ; almost smooth in the medio-dorsal region ; the rest of 

 the valve ornamented with concentric slender growth-ridges 

 and striae ; the ridges are fewer, thicker, and wrinkled on the 

 anterior angulation, those on the posterior carination are 

 obliquely striated. 



The pallial line is very broad and near the margin, the 

 siphonal inflection is horizontal, rounded at the end, and ex- 

 tends to a little more than one-fourth the distance between the 

 adductor scars. 



