DESCRIPTIONS OF NEW SODTH WALES FOSSILS ETHERIDGE. 225 



Paracyclas (?) obliqna, tip. tiov. 



(Plate xl., figs. 6 and 7). 



Sp. Clmrs. — Shell broadly elliptical, slightly oblique to the 

 posterior; length considerably exceeding the breadth; valves 

 eqiiail}" convex, inclined to gibbosity in the centres. Cardinal 

 margins less than the width of the shell, faintly ai-ched ; 

 anterior, posterior, and ventral margins rounded ; anterior and 

 posterior slopes ill-defined ; ligamental gi-ooves (one in each 

 valve) rather faintly marked and shallow. Concentric costse 

 remarkably regular, and in testiferons examples must have 

 been prominent and strong, with traces of interlineations. 



Obs. — The obliquity to the posterior distinguishes this from 

 most of the American species. An Australian ally may be found 

 in De Koninck's Sculdia (.'') lamellifera}^ but our little shell is 

 certainly not a Sciddia. 



Genus [Allorisma], KiiKj, 1844 and 1850. 



(Annals Mag. Nat. Hist., xiv., 1844, p. 315; Mon. Permian 

 Foss. England, 1850, p. 196). 



In 1844 Prof. W. King proposed liis Allorisma without 

 naming a type, as a genus of Pholadomyidae, both valves being 

 furnished with a cartilage fulcrum elongated in the direction 

 of the cardinal line ; also described as edentulous, and the 

 pallial line indistinct. 



In the second definition published in 1850, the valves were 

 said to articulate " by means (only) of an external cartilage," 

 and the pallial sinus deep or shallow ; Hiutella sulcata, Fleming, 

 was named as the type species. 



Without entering into a mass of historical detail, it is 

 sufficient to point out that King's definitions are diametrically 

 opposed to one another. An author cannot be allowed to play 

 fast and loose, even with genera of his own proposing, without 

 endless confusion arising, and such confusion has arisen, for no 

 two authoi's use the name Allorisma in the same sense, one 

 employs it in the sense of 1844, another in that of 1850. 



McCoy claimed!*^ that, as originally defined Allorisma was, 

 in part at least, the equivalent of his Sanguinolifes ; probably 

 so, but those species included in the second definition of the 



15 De Koninck — Foss. Pal. Nouv. Galles dii Sud, pt. 3, 1877, pi. xv., 

 fig. 7. 



IB McCoy— Brit. Pal. Foss., fas. ii., 1852, p. 276. 



