126 PERMIAN FOSSILS. 
Now as the typical species (Avomites exporrectus, Wahlenb.) of Dalman’s Cyrtia agrees 
with the type of Sowerby’s Spirifer im 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, Ihave been led to adopt it in 
preference to the one proposed by Dalman. This enables me to retain for another 
group of Sprriferide a name which many conchologists have considered as a cancelled 
synonym. 
Genus Trigonotreta, Keenig.” 
SPIRIFER, Auct. 
Cuoristites, Fischer de Waldheim, 1825. 
Detruyris, Dalman, 1827. 
Bracuytuyris, M‘Coy, 1844. 
SPrRIFERINA, 4. d’ Orbigny, 1848. 
Diagnosis —“ Vesta inzequivalvis, plana aut lobata; valvarum altera superne pro- 
ducta in rostrum externe convexum, interne planum, perforatum, subtriangulare ; 
cardo infra foramen, plerumque linearis, strictus.” (Koenig.)’ 
This genus differs from Spirifer in having generally incurved umbones, and a non- 
foraminated deltidium. 
The present section of Spiriferide has been divided by various parties into two or 
more genera, as Choristites, Brachythyris (which are the exact equivalents of 7rzgonotreta), 
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 Spiriferide, with large punctures, such as Zrigonotreta Walcott, are 
generically distinct from those which have hitherto been considered as non-punctated :* 
but having arrived at the conclusion that all Spiriferide 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 7. Walcott and T. cristata ; but the 
distinction, as founded on this association, is evidently fallacious, since a median plate 
1 Dr. Carpenter states that Spirifer cuspidatus is a non-punctated shell, which I suspect is an oversight. 
The punctures are very distinct in Spirifer heteroclytus. Ihave not had an opportunity of examining a 
specimen of Spirifer exporrectus. 
2 T do not know the date of Trigonotreta: it is assumed to have been published prior to 1825, 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 Productus 
Hoppi), was published in 1825. (Vide Mon. du Genr. Productus, pp. 80, 267.) 
3 Tcones Fossilium Sectiles, p. 3. 
4 T entertained this view when my Synoptical Table went to press—this will explain the recognition 
therein of Delthyris. 
