120 DEVONIAN FAUNA. 



1. AcTiNOCERAs DEVONiCANs, B. sp. Plate XII, figs. 8, 8 a. 



Cf. 1840. Oethoceeatites elliptioijs, Munster. Beitrage, pt. 3, p. 96, pi. xviii, fig. 2. 

 1841. Obthocebas Ltjdense, Fhil. (not Sowerby). Pal. Toss., p. 110, pi. xlii, 



fig. 206. 



Description. — Shell large, smooth?, tapering rapidly. Septa rather narrow, 

 very convex. 



Size. — 34 mm. in greater and 28 mm. in lesser diameter. 



Locality. — Lummaton. 



BemarJcs. — There are in my Collection two specimens from Lummaton which 

 show the convex wall of the chamber of a large Cephalopod, but which are in both 

 cases too imperfect for any description. The section of one of them is very elliptic 

 and its septa transversely oblique, but this possibly is due to distortion, from which 

 the specimen has evidentlyto some extent suffered. The siphuncle is large and shows 

 some indistinct and doubtful signs of radiation. The external surface appears to 

 be smooth. A comparison of the two specimens would point to the presumption 

 of an oblique, elliptic, and very conical shell. The most interesting point about 

 them, however, is that they show rough deposits by the mantle of what originally 

 was organic matter, as pointed out by Barrande^ in his notes on some plates of 

 Orthoceras. In 0. Ludense, Phillips, not Sowerby, which is quoted by Phillips 

 from Marwood and South Petherwin, the section given by Phillips shows the 

 siphuncle to have been, as in ours, somewhat laterally excentric, and I see no 

 reason for doubting that they specifically agree. 



Affinities. — These specimens may be compared with 0. ellipticiis, Miinster,' 

 which is a very transverse species. The section in our fossils is more transverse 

 than in Phillips's figure, but not nearly so much so as in Miinster's, the ratios of 

 the diameters being respectively four-fifths, three-fourths, and about two-thirds. 

 0. Ludense, Sowerby,^ is a perfectly distinct shell, and has a circular section. 



0. omissum, Blake,* seems a kindred form, being elliptic in section, but the 

 siphuncle is much nearer to the lateral margin. 



VII. Family. — Orthoceratid^. 



1. Genus. — Orthoceras, Breyn, 1732. 



This is the largest and one of the best defined genera in the Nautiloidea. 

 Foord thus defines it : " Shell straight or slightly curved, elongate-conical, circular 



1 1865, Barrande, ' Syst. Sil. Boheme,' vol. ii, pi. ccxxviii, figs. 5—8, and pi. ccxxix, figs. 2 — 10. 



2 1840, Miinst., ' Beitr.,' pt. 3, p. 96, pi. xviii, figs. 2 a, h. 



3 1839, Sovsrerby in Murcbison's ' Sil. Syst.,' p. 619, pi. ix, fig. 1. 



4 1882, Blake, ' Men. Brit. Poss. Cepb.,' p. 160, pi. xv, figs. 9, 9 a. 



