126 PERMIAN FOSSILS. 



Now as the typical species {Anomites exporredus, Wahlenb.) of Dalman's Cyrtia agrees 

 with the type of Sowerby's Spirifer in form, and in being possessed of a foraminated 

 deltidium (vide ante, p. 124)/ I am led to assume that both these genera are one and 

 the same ; and as the latter name has the priority, I have been led to adopt it in 

 preference to the one proposed by Dalman. This enables me to retain for another 

 group of Spiriferida a name which many conchologists have considered as a cancelled 

 synonym. 



Genus Trigonotreta, Koenig.^ 



Spiuifer, Anct. 



Choristites, Fischer de Waldheim, 1825. 

 Delthyris, Balman, 1827. 

 Brachythyris, M'Coy, 1844. 

 Spikiferina, a. d'Orbigny, 1848. 



Diagnosis. — " Testa insequivalvis, plana aut lobata ; valvarum altera superne pro- 

 ducta in rostrum externe convexum, interne planum, perforatum, subtriangulare ; 

 cardo infra foramen, plerumque linearis, strictus." (Kcenig.)^ 



This genus differs from Spirifer in having generally incurved urabones, and a non- 

 foraminated deltidium. 



The present section of Spiriferida has been divided by various parties into two or 

 more genera, as Choristites, Brachythyris (which are the exact equivalents of Triyonotreta), 

 Delthyris, and Spiriferina (apparently the counterparts of each other). I have for some 

 time past entertained the idea that the two groups thus indicated had each a generic 

 value, — that the Spiriferida, with large punctures, such as Triyonotreta Walcotti, are 

 generically distinct from those which have hitherto been considered as non-punctated :* 

 but having arrived at the conclusion that all Spiriferida have a punctured structure, 

 I have been compelled to abandon this idea : further, the presumed generic distinction 

 appeared to be supported by the median plate, situated between the dental plates, being 

 associated with the punctured structure, as in T. Walcotti and T. cristata ; but the 

 distinction, as founded on this association, is evidently fallacious, since a median plate 



^ Dr. Carpenter states that ^Spiri/er cmpidatus is a non-punctated shell, which I suspect is an oversight. 

 The punctures are very distinct in Spirifer heteroelytus. I have not had an opportunity of examining a 

 specimen of Spirifer exporredus. 



2 I do not know the date of Trigonotreta : it is assumed to have been published prior to 1 825, the year 

 in ■which Fischer de Waldheim described his genus Choristites; since it was published in the first .part 

 (Centuria Prima) of the ' Icones,' which it is reasonable to suppose appeared before the second, which, ac- 

 cording to De Koninck (who notices this part in consequence of its containing a description of Produetua 

 Hoppi), was pubhshed in 1825. (Vide Mon. du Genr. Productus, pp. 80, 267.) 



^ Icones Fossilium Sectiles, p. 3 



* I entertained this view when my Synoptical Table went to press — this will explain the recognition 

 therein of Delthyris. 



