ANIMALS. 193 



ScHizoDUS TRUNCATUS, King. Plate XV, figs. 25, 26, 27, 28, 29. 



(?) AxiNUS OBSCUEUS, J. Sow. Mill. Conch., No. 55, p. 12, pi. 314, lowest figure, 1821. 

 (?) Venus (?), J. de C. Sow. Trans. Geol. Soc. Lond., 2d series, vol. iii, p. 120, 1829. 

 (?) — (?) „ De laBeche, Geol. Man., p. 385, 1831; Germ. Transl., 



p. 459, 1832 ; 3d Eng. ed., p. 573, 1833. 

 AxiNUS (SCHIZODUS) TRUNCATUS, Einff. De Verneuil, Bull. Soc. Geol. de France, 2"" 



serie, vol. i, p. 31, 1844. 

 — ( — ) — „ Geol. Russ., vol. i, p. 224, 1845.. 



ScHizoDUS — „ Tennant, Strat. List, p. 88, 1847. 



— — „ King, Catalogue, p. 11, 1848. 



AxiNUS — „ Howse, Trans. T. N. F. C, vol. i, pp. 245-6, 



1848. 



Diagnosis. — Moderately inequilateral, the posterior side being the longest : a little 

 wider than long, the width being an inch, and the length seven eighths : marked with 

 dark spots on a light-coloured ground : finely threaded parallel to the margins, more 

 decidedly on the anterior than on the posterior half: moderately tumid in the umbonal 

 region : slightly tapering, and rather obliquely truncated, at the posterior side : 

 regularly rounded anteriorly. 



This remarkably pretty species differs from ScMzodus ohscurus in having thinner 

 valves, the anterior half not so deep longitudinally, and the posterior half decidedly 

 less acuminated : the last difference is caused by the slighter obliquity of the dorsal 

 and posterior margins, and the more evenly and less rounded form of the ventral 

 margin, as displayed in fig. 25, PI. XV, which is a correct representation of the species. 

 The small Russian Permian specimen represented in the ' Geology of Russia,' vol. ii, 

 pi. xix, fig. 8, and considered by M. de Verneuil to be a variety of Schizodus Rossicus 

 (p. 310), seems to be nearly allied to it; judging from some casts which I have 

 examined belonging to the cabinet of Sir Roderick Impey Murchison. 



Occasionally specimens occur showing marks of their original colours (vide PI. XV, 

 fig. 28), which consist of small oblong dark spots on a light ground, resembling what is 

 generally displayed on the recent Circe Castrensis} 



Its dental system, already described, is pretty correctly represented in Plate XV, 

 fig. 29. 



Schizodus truncatus is rather a scarce fossil : specimens are found at Humbleton 

 Quarry, Tunstall Hill, Silksworth, and Whitley Quarry in shell limestone. 



^ Marks of colour occur in other Permian fossils, as Pleurotomaria antrina, Schl., Natica Leibnitziana, 

 &c. Professor Phillips has represented a heautifully-marked specimen of Pleurotomaria carinata. Sow. 

 But the most striking instance of the kind that I have seen is on some of my specimens of a Carboniferous 

 Pecten, which has wide red-coloured bands radiating from the umbones. 



