18 
^TAtrilTiOIDEA. 
SILURIAN SPECIES. 
Orthoceras primsevum, Forbes. 
1845. Creseis primceva, Forbes, Quart. Journ. Geol. Soc. vol. i. 
P- 146. 
1846. Creseis primceva, Sbarpe, Quart. Journ. Geol. Soc. toI. ii. 
pi. xiii. f. 2. 
1846. Creseis ventricosa, Sharpe, loc. cit. pi. xiii. f. 3. 
1852. Orthoceras primcemm, MUoy, British Pal. Foss. fasc. ii. 
p. 316. 
1852. Orthoceras primcevum, Salter, in McCoy’s British Pal. Foss., 
Appendix A, p. viii. 
1852. Orthoceras rentricosum, M‘Coy, British Pal. Foss. fasc. ii. 
p. 318. 
1852. Orthoceras ventricosum, Salter, in McCoy’s British Pal. Foss., 
Appendix A, p. vii. 
P 1852. Orthoceras torquatumy Salter, in McCoy’s British Pal. Foss., 
Appendix A, p. yii. 
1857. Orthoceras primcevum, Salter, in Murchison’s ^ Siluria,’ Foss. 
Gr. 62. f. 4. 
1873. Orthoceras primcevum, Salter, Cat. Cambr. and Silurian Foss, 
pp. 97, 159. 
1873. Orthoceras ventricosum, Salter, Cat. Cambr. and Silurian Foss, 
pp. 98, 159. 
P 1873. Orthoceras torquatum. Salt. Cat. Cambr. and Sil. Foss. p. 187. 
1882. Orthoceras primmmm, Blahe, British Foss. Ceph. pt. i. p. 148, 
pi. xiii. f. 4. 
Sp. Char. The rate of increase is difficult of determination 
owing to the compression of the specimens ; it varies from 1 in 5 to 
1 in 9 (0. ventricosum)^ but becomes in the other form {0. 
primcevum) reduced to 1 in 18. The septa (about which there 
appears to be some doubt) are stated by Professor Blake to be 
distant y to | the diameter, with a slight obliquity. The same 
author remarks that “ the body-chamber was probably very long.” 
Siphuncle minute and central. Surface with tranverse striae, too 
obscure to be characterized. 
BemarTcs. These are very obscure fossils. None of the speci- 
mens known as 0. ventricosum are to be found in the National 
Collection, and I have derived my information regarding this form 
from Professor Blake’s description of the species. 
Horizon. Wenlock Shales. 
■ Locality. Nantglyn, Denbighshire. 
This species is fairly well represented. 
