ORTHOCERAS. 125 



? ? 1870. Oethoceeas lineatum, Barrande. Syat. Sil. Boheme, p. 70i, pi. ccccxxxviii, 



figs. 1 — 5. 

 ? 1882. — — var. tenuisteiatum, BlaJce. Mon. Brit. Ceph., 



p. 128, pi. vii, figs. 7, 13. 

 1889. — TENnsTEiATUM, WJiidl. Geol. Mag., dec. 3, vol. vi, p. 30. 



BescripUon. — Shell straight, elongate, conical. Section circular. Siphuncle 

 central. Ratio of tapering 1 : 6. Surface covered by very fine and regular 

 sharp longitudinal strire, divided by concave interspaces, visible only through a 

 lens, and numbering about 150 near the mouth. 



Size. — The figured specimen measures 45 mm. in length and 12 mm. in 

 diameter at the upper extremity. 



Locality. — Wolborough ? There is a single specimen in the Torquay 

 Museum, which, as far as can be judged from the matrix, came from that locality. 



Remarks. — This unique specimen is in a fine state of preservation ; the minute 

 ridges come out clearly under a lens, in spite of their great number, and there are 

 even indications of a still finer cross lineation beading the rays. 



Mr. Roberts has kindly verified this identification for me, and believes it to be 

 correct. In fact, in the shape, size, and character of ornamentation Miinster's 

 figure appears to us to agree perfectly with the present shell. 



The only species that approaches it at all nearly among those found in Devon- 

 shire is, as far as we know, 0. eutrichum, Whidborne, but this is distinguishable 

 by the much greater coarseness and fewness of its markings, which are visible to 

 the naked eye. Although the chambers are not seen, there are indications in the 

 specimen leading to the belief that they were extremely narrow, and hence it would 

 have been satisfactory if we had a specimen of the exterior of the British shell 

 referred by Phillips to 0. imbricatum, Wahl.,^ with which to compare it. 



Miinster points out that it differs from his other species, 0. striato-punctatiim,^ 

 in its much more elongate shape, though he thinks that young specimens of the 

 latter, deprived of their outer shell, might be confused with it. 0. conoideum^ 

 Miinster, as represented by a specimen in the British Museum, differs from it by 

 being quite smooth, and 0. semipUcaium, Miinster,* in being, according to the 

 description, smooth on one side and having transverse folds on the other, but 

 without longitudinal markings. 



0. Darwini, Billings,^ has much coarser lineations, and is slightly curved. It 

 is from the Silurian of Canada. 



1 1821, "Wahl., ' Nova Act. Soc. Tpsal.,' vol. viii, p. 89. 



2 1840, MuDst., ' Beitr.,' pt. 3, p. 101, pi. xx, figs. 1—3. 



3 Ibid., p. 96, pi. xviii, figs. 4, 5. * Ibid., p. 98, pi. xviii, fig. 7. 



5 1862, Billings, 'Pal. Toss.,' vol. i, p. 161 ; and 1888, Foord, 'Cat. Ceph. Brit. Mus.,' vol. i. 

 p. 76, fig. 8. 



