HARPOCERAS STRIATULUM. 451 



the Lyt. Jurense zone at Frocester Hill, from whence the shell drawn on PI. LXIV, 

 figs. 1 — 3 was collected ; the large specimen, figs. 5, 6, 7, on the same Plate, was 

 obtained from the equivalent horizon in Germany, the locality is unfortunately not 

 recorded. I have a beautiful specimen from the Upper Lias of Somersetshire, depicted 

 on PI. LXXXI, fig. 4. Most of the examples of Harpoceras radians from Frocester and 

 Nailsworth Upper Lias Sands are small, compressed, thick, stout shells. 



Harpoceras striatulum, Sotoerbi/. PI. LXXXIV, figs. 4, 5, 6. 



Ammonites striatdlus, Sowerby. Min. Conchol., vol. iv, p. 23, tab. 421, 



fig. 1, 182.?. 



— LINEATUS, Schlotheim. Petrefactenkunde, p. 75, No. 24, 1820. 



— — Zieten. Verstein. Wiirtembergs, p. 12, pi. ix, fig. 7, 



1830 



— STRIATULUS, — Ibid., p. 1 9, pi. xiv, fig. 6, 1 830. 



— CoMENSis, Von Buck. Petrif. remark, pi. ii, figs. 1 — 3, 1831. 



— Thouarsensis, d'Orbigny. Terr. Jurass., p. 222, pi. 57, 1842. 



— RADIANS DEPRESSES, Qiietistedt. Cephalopoden, tab. vii, figs. 4 — -6, 1849. 



— CoMENSis, Chapuis and Dewalque. Mem. Cour. Acad. Roy. 

 ' Belgique, t. xxv; Fossil Luxembourg, p. 63, 



pi. ix, fig. 1, 1854. 



— STRIATULUS, Simpson. Fossils York. Lias, p. 87, 1855. 



— — Oppel. Die Juraformation, p. 248, 1856. 



— — Bumortier. Depots Jurassiques, partie iv, p. 64, 



pi. xvi, fig. 1, 1874. 



— Thouarsensis, — Ibid., p. 63, 1874. 

 Harpoceras striatulum, Tate and Blake. Yorkshire Lias, p. 308, 1876. 



Diagnosis. — Shell discoidal, depressed, carinated ; whorls about one third involute, 

 convex on the sides ; radii short ; biflexed slender, vanishing from the inner third, thereby 

 producing a smooth open umbilicus ; siphonal area narrow, sloping towards the sides ; 

 radii terminate near the keel, which is small, trenchant, and bounded by two shallow 

 sulci. Aperture elliptical ; suture-line tortuous ; septa wide apart. 



Dimensions. — Transverse diameter 60 millimetres; width of the umbilicus 25 milli- 

 metres ; height of aperture 18 millimetres; width of aperture 13 millimetres. 



Description. — This Ammonite, evidently the Am. radians depressus, Quenst., and 

 Am. Thouarsensis, d'Orbig., is easily distinguished from Am. radians, Reinecke, by 

 the smooth inner portion of its convex whorls, from which the ribbing is absent, a 

 character Sowerby failed to delineate in his otherwise good figure. The other 

 point to which he attached so much importance, and upon which he founded the 

 name striatulus, is seldom present, as the striae only exist on the outer lamina of the shell 

 which is seldom preserved. The baldness of the inner side of the whorl is a most 

 persistent character, as the several specimens before me from different localities satis- 



