124 PERMIAN FOSSILS. 



and Pentamerus, and certain Orthises.^ The socket-plates appear to be in general 

 only slightly developed. 



The fissure in Spiriferida possesses a variable character, being closed by the 

 deltidium in the t5rpical genus ; also in certain species of Trigonotreta [T. rostrata and 

 T. speciosa) ; but it is well known to be open in others. It appears to be closed, when 

 the shell is young, in Trigonotreta cyrtana, and afterwards to become open :^ on the 

 contrary, in Trigonotreta undulata it is open when youngs and closed when old. 



Spiriferida are not generally foraminated : two or three genera are character- 

 istically so, and another only thus partially. In Spirifer the foramen passes through 

 the deltidium -.^ in Betzia it is complete, and situated at or near the point of the umbone, 

 as in Terehratula : while in Atrypa {Reticularis) the same part is similarly foraminated ; 

 but only in certain varieties. 



The present family differs remarkably from its equivalent and associated groups in 

 rarely exhibiting traces of the vascular system ; as the only specimen I have seen 

 displaying them is the one represented in fig. 6 c, PI. IX. 



The histology of Spiriferidce offers certain modified characters, which, however, 

 are not of such a nature as is generally supposed. Dr. Carpenter has noticed 

 " perforations very well marked in Spirifer Walcotti of the Lias, while they are absent 

 in Spirifer cuspidatus, and another mountain-limestone species, and in a species from 

 the Devonian formation of Hudson's Bay."* These perforations or punctures have 

 been long known to me, as occurring in certain Permian species ; and they have been 

 recently noticed by Dr. de Koninck, who says, " in the genus Spirifer several species 

 are known to have the shell perforated, as in certain Terebratula : these species 

 constitute the genus Spiriferina of M. d'Orbigny : the Spirifer cristatus, Schl., is in 

 this case : this species I have found among the fossils of M. Roberts ;* and as none of 

 the perforated Spirifers have yet been found in the carboniferous rocks, we are 

 warranted in concluding that the Palaeozoic fossil beds of Spitzbergen belong to the 

 Permian epoch.^ 



But unfortunately for Dr. Carpenter's observation, and Dr. de Koninck's^ con- 



1 Vide Ann. and Mag. of Nat. Hist., vol. xviii, p. ^Q, 1846, 



2 This character of the fissure is supported by some unpublished figures of Trigonotreta cyrtcena executed 

 in lithograph by Mr. T. Davidson. 



^ In Spirifer heteroclytus the deltidium is convex or ridge-like on its inferior half, and concave or 

 furrowed on its upper half : the foramen is situated at the base of the furrow, and passes behind the ridge. 



* Report of the Fourteenth Meeting of the British Association, p. 18, 1845. Dr. Carpenter states that 

 Mr. Morris had noticed the like difference in other Spiriferidce. 



^ M. Roberts's fossils were collected at Spitzbergen, among which, according to Dr. de Koninck, are 

 Trigonotreta undulata and Strophalosia Cancrini. 



^ Vide Bulletin de la Soc. G6ol. de France, 2""^ serie, t. vi. Seance June 2, 1849. 



7 In some specimens of a carboniferous Trigonotreta coUected in Belgium, and given me by Mr. T. 

 Davidson, the punctures are as visible as in T. cristata. I believe the specimens referred to have been 

 identified by Dr. de Koninck with the last species ; but they are certainly distinct. 



