OfilHOCERATID^. 
123 
Ortho c eras ?, sp. 
1854. Cyrtoceras unguis ?, F. Roemer, Palseont. Bd. iii. p. 93, t. xiii. f. 28. 
1877. Cyrtoceras unguis ?, Barrande, Syst. Sil. de la Bolieme, vol. ii. 
Supplem. pi. cccclxxxvii. case xi. ff. 1, 2. 
Two small fragments of the apical portion of a rather rapidly 
tapering shell with a subcentral siph uncle, septa moderately distant, 
and line transverse undulating striae, not quite parallel with the 
septa ; the latter bend very sharply upwards at the sides. The 
test is very thin, so that the septa are seen through it. 
Remarhs. MM. Roemer and Barrande represent this species with 
the striae quite parallel with the septa, which is not the case with 
the specimens in the National Collection. The present form bears 
some resemblance to 0. teres, Sow., but the sculptui’e of the latter 
consists of strong riblets, and it appears also to taper less rapidly. 
Horizon. Lower Limestone Group h 
Locality. Lanark? 
Represented by two specimens in the Collection. 
Orthoceras sulcatum, Fleming. {Ante, p. 108.) 
Among the specimens of 0. sulcatum occurring at this horizon are 
several very small ones, which have proved upon examination to 
to be the young shells. Their ornamentation 
is so peculiar as to merit description. It con- 
sists of faint, rather distant annulations, 
covered, together with their interspaces, by 
fine, transverse, thread-like lines, crossed 
longitudinally by similar, but somewhat more 
prominent raised lines, giving a finely cancel- 
lated appearance to the surface when viewed 
under a lens. Soon, however (within a dis- 
tance of six or eight lines), the annulations 
grow more prominent, the longitudinal lines 
suddenly become obsolete, and the ornamenta- 
tion assumes the aspect of the adult shell. 
This remarkable alteration in the sculpture 
of the test was obseiwed by Barrande in a 
species which he named 0. pseudocalamiteum 
(p. 62). This also had in the very young 
state {i. e. for a distance of about seven lines 
from the initial point) a cancellated orna- 
mentation, which abruptly gave place to the 
Fig. ^.— Orthocer as sulcatum. Apical extremity, showing the 
ornamentation of the test in the young shell; enlarged. 
1 Carboniferous Limestone Series (see footnote, p. 121). 
