370 Reviews — Barrande's Silurian of Bohemia — 



Considering the divergence of opinion among authors with regard 

 to the relationship and classification of recent mollusca of which they 

 have complete representatives, it is not surprising that they should 

 differ when they are dealing with the imperfect remains of past ages. 

 Thus palaeontologists are at variance as to the genera they include in 

 the Capulidae, Cuv., as some of the forms referred to it approach the 

 Naticidse and others the Neritidae. Perner places in that family the 

 following sis Bohemian genera, containing 188 species and extending 

 from E-e 1, to G-g 3 : Platyceras, Conrad; Orthonychia, Hall; 

 Platyostoma, Conrad; Strophostylus, Hall; Cirropsis, Pern.; and 

 Naticonema, Pern. Perner separates from the Tertiary and recent 

 genus Capulns, Montf., Palaeozoic forms greatly resembling it, and 

 groups them in the genus Platyceras, Conrad (Acroculia, Phill.). This 

 genus is limited to shells distinctly spirally coiled, while Orthonychia, 

 Hall, is reserved for those forming a straight cone whose apex is 

 simply or slightly curved on the same plane. The number of forms 

 belonging to these two genera is immense ; Barrande's MS. enumerates 

 400 species, which are represented on 150 plates, more than half the 

 number of species intended for the three ' tomes ' of vol. iv. Since his 

 time specimens have accumulated, and in the midst of such wealth of 

 material it has been difficult to decide on the limits of a species, for 

 a considerable extent of variation exists on the one hand, while on 

 the other there are strong connecting links. Though not reducing 

 the number of species to such a degree as Lindstrom does for Gotlandic 

 forms, Perner yet brings them down to 98 for Platyceras, of which 

 96 are new, and 45 for Orthonychia, of which 41 are new. There are 

 besides numerous varieties and some doubtful species not included in 

 the above numbers. Platyceras is most abundant in the Silurian (E), 

 while the greater number of Orthonychia occur in the Devonian 

 (F-f2), generally in the condition of internal moulds. Dr. Perner 

 finds it convenient to divide these two genera into groups of species, 

 each associated with a characteristic form. 



Naticonema, Pern., is distinguished by its flat, discoidal shape, 

 without umbilicus, slightly thickened inner lip with thin, vertical 

 lamella, and by its longitudinal prominent scaly striae. N. similare, 

 Barr., the only Bohemian species, is the genotype. It comprises, in 

 addition to his Otospira squamata, 1 shells referred by Barrande to no 

 less than seven different species belonging to six distinct genera. 

 Amongst foreign forms Dr. Perner would place in this genus some 

 specimens figured by Lindstrom as Platyceras cornutum. His Natico- 

 nema is confined to E-e 2. 



Cirropsis, Pern., comprises more elongated shells with the general 

 appearance of Holopea. They are distinguished by their loosely coiled 

 whorls, oblique and unthickened aperture, and by the direction and 

 nature of their transverse ornamentation. Numerous species were 

 described by Barrande in MS., and referred by him to Cirrus. These 

 are reduced by Perner to five, and are shown to differ from Cirrus in 

 the form of the aperture and ornamentation. This genus occurs in 

 E-e 1, and e 2 (Sil.), and is represented both in Gotland and America. 



1 Spelt by Perner squammata. 



