320 Mr. J. Morris on the genus Siplionotreta. 



careo -corneous, more solid than Lingula, but closely allied to it, 

 and differing from it in having one valve with a slight furrow for 

 the passage of the pedicle, as well as some modifications in the 

 interior structure of the valves. 



The group of the Siphonotretese, Kut., are arranged by M. 

 D'Orbigny, under the families Lingulidse and Orbiculidse, in his 

 first great division of Brachiopoda, with the following characters 

 (Comptes Rendus, vol. xxv. p. 267, Aug. 1847) : — 



Lingulida. A pedicle or exterior muscle passing between the valves ; 



shell corneous ; animal fixed. 

 The beaks of both valves hollowed with a furrow for the passage of 



the muscle Lingula, Brug. 



The beak of one valve only with a furrow for the passage of the 



muscle Obolus, Eichwald. 



Orbiculidce. The muscle passing out by the inferior valve ; shell 



free. 

 Shell testaceous, perforated ; muscle of attachment pedunculated, 



placed at the summit of the beak. . Siphonotreta* , De Verneuil. 

 Shell testaceous, perforated ; muscle of attachment placed by the 



side of the beak Orbicella f, D'Orb. 



Shell corneous, not perforated ; muscle pedunculated. 



Orbiculoidea, D'Orb. 

 Shell corneous, not perforated ; muscle not pedunculated. 



Orbicula, Lam. 



From the above general remarks, it will be evident that the 

 four genera above mentioned cannot properly be arranged in 

 the same family of which Siphonotreta is the type, and from 

 which the other three are readily distinguished ; in fact, as pre- 

 viously observed, they belong to four distinct groups ; Siphono- 

 treta being allied to Crania, Schizotreta to Orbicula, Aulonotreta 

 to Lingula, and Acrotreta probably identical with Cyrtia. 



I shall conclude these notes with the following brief descrip- 

 tion of the new species of Siphonotreta : — 



Siphonotreta anglica. PL VII. fig. 1 a-e. 



Shell of a rather oblong-oval form, depressed, marked by the 

 fine lines of growth ; surface minutely but concentrically reticu- 



* Mr. W. King places Siphonotreta in the family Craniidae. 



f Orbicella, D'Orb. (Aug. 1847), is stated by Mr. Davidson, ' Bull. Geol. 

 Soc. France,' n. s. vol. v. p. 315, to be identical with the genus Trematis, 

 Sharpe (June 1847). This can scarcely be the case, if both genera are cor- 

 rectly described ; for Orbicella is placed by D'Orb. among the hingeless Bra- 

 chiopods, whereas Mr. Sharpe describes Trematis as having a hinge. The 

 two diverging plates in the non-perforated valve of Trematis are somewhat 

 remarkable, as, where they exist in other Brachiopoda, they always form 

 internally the margins of the deltidial area, partly protecting the passage for 

 the muscle of attachment, and forming the dental processes of the hinge. 



