I5S- 



V. Spirifer disjunctus Sow, and Cyrtia murchisoniana DeKon. 



In the present paper Cyrtia murchisoniana is mentioned as synonymous - 

 with Sj^irifcr disjunctus var. sub-archiaci. The writer's intention, however, 

 is not to put all the fossils ever recorded as Cyrtia murchisoniana under 

 Spirifer. It is only the Uralian form described by Tscheknyschew that is to- 

 be so treated. 



According to Schuchert, Cyrtia is a genus distinct from Spirifer with- 

 in the Sub-family Spiriferinae. It is distinguished from Spirifer by having 

 an unusually high ventral area, with its narrow delthyrium closed by a per- 

 forated pseudodeltidium, resulting from fused deltidial plates." Notwith- 

 standing, there are such forms among the species of Spirifer which have an- 

 equally high ventral area, as for instance, Spirifer disjunctus Sow, of the 

 Devonian, and Spirifer distana Sow, and Sp. cuspidata Martin of the 

 Carboniferous. Thus the height of the ventral area seems not very im- 

 portant as a generic characteristic. 



As to the perforated pseudodeltidium Schuchert's idea represents the 

 general opinion concerning its systemtic significance. In the course of his 

 description of Spirifer cuspidatus Sow., D.widson discards M'Cov's view ofo 

 the species as a Cyrtia : he says, " No specimen of Sp. cuspidata I have 

 hitherto been able to examine has exhibited the deltidium in its entire condi- 

 tion, but which, in all probability, was not perforated by a circular foramen, as 

 is in true types of the subgenus Cyrtia, such as C. trapezoidalis and C- 

 Murchisoniana." 



In the .same work Davidson observes that Sp. cuspidata may have a per- 

 forated pseudodeltidium. He says, " Subsequeutly, however, Mr. J. P. 

 Woodward show^ed me the internal cast of the ventral of a specimen in the- 

 British Museum, thought to have belonged to Sp. cuspidata, and de- 

 rived from the dolomitic Carboniferous limestone of Breedon hill in which 

 there is evidence that the deltidium was in reality perforated by a circular 

 foramen, as in Cyrtia.'' Thus it seems that M'Cov's opinion which was first 

 rejected by Davidson in the text after all proved to be correct. It, is, how-- 

 ■ever, not certain whether the specimen Woodward showed to Davii son was 



