ANIMALS. 127 
is present in Zrigonotreta cyrtena,' and T. attenuata,’ which, from their punctures being 
so small as to be with difficulty distinguished, would doubtlessly be placed among the 
non-punctated Spiriferide. 
After a careful consideration of the present subject, I am led to believe that it will 
be the most advantageous plan to group all those Spiriferide in Trigonotreta having 
an area, regardless of its width; the valves ribbed or striated; and the large valve 
furnished with dental plates, and occasionally a median plate, irrespective of their size. 
Choristites Mosquensis, Waldh., and Spirifer undulatus, J. de C. Sow., according to 
this view, are generically inseparable ; as the long dental plates of the first are merely 
enlargements of their rudimentary homologues in the last: ASpirzfer princeps, M‘Coy, 
and Brachythyris planicostata, M‘Coy, are also referable to one and the same genus ; 
the one having simply a greater lateral development than the other: while Spzrifer 
Walcott, and Delthyris cyrtena,? are equally unseverable; because the large median 
plate of the former is more developed than its homologue of the latter. 
The foregoing remarks will explain my reasons for declining to adopt, at least for 
the present, M. d’Orbigny’s Sporiferina. 1 cannot but express my doubt of their being 
any structural difference between it and Zrzgonotreta: they appear to be separated 
merely by differences in the development of their respective structures, which it is 
evident have little or no value in a generic point of view. 
TRIGONOTRETA CRISTATA, Schlotheim. Plate VIII, figs. 9, 10, 11, 12, 13, 14. 
(?) OsTRACITES CRISTA PULLI, Sch7. Leonhard’s Taschenbuch, vol. vii, p. 76, 1813. 
TEREBRATULITES CRISTATUS, Schl. Akad. Miinch., vol. vi, p. 28, pl. i, figs. 3 a, 6, c, 1816. 
= om »  Petrefactenkunde, p. 265, 1820. 
— a »  Boue, Edin. Phil. Journ., vol. xii, p. 144, 1825. 
(?) = PECTEN >  Boue, Loe. cit. 
TEREBRATULA CRISTATA » De la Beche, Geol. Man., Ist ed., p. 384, 1831; 
Germ. Transl. p. 459, 1832; and 3d Eng. ed., 
p. 573, 1833. 
SPIRIFER OCTOPLICATUS, J. de C. Sow. Von Buch, Ueber Delthyris, p. 39, 1834. 
TEREBRATULA crisTaTA, Schl. Phillips, Encye. Met., vol. iv, p. 617, 1834. 
SPIRIFER CRISTATUS »,  Quenstedt, Wiegmann’s Archiv, p. 79, 1835. 
TEREBRATULA CRISTATA ,, Thomson, Outlines of Min. Geol., &., vol. ii, p. 324, 1836. 
SPIRIFER CRISTATUS (partim), Schl. Le Cocq., Mém. Géol. Soc. de France, t. iv, 
p- 185 (excluding the figures).4 
1 The median plate is displayed in an unpublished figure of the internal structure of this species by Mr. 
T. Davidson. 
2 Vide M‘Coy’s Synopsis of the Characters of the Carboniferous Fossils of Ireland, p. 127, fig. 14. 
* J have seen species with the median plate of a more rudimentary form than in Delthyris cyrtena ; 
but I have not been able to ascertain their specific name. 
+ The figures appear to be copies of J. Sowerby’s Spirifer octoplicatus (Min. Conch., pl. 562, figs. 2, 3). 
