298 PAL/EONTOLOGY OF NEW YORK. 



No author has been in a more favorable position for the study of Pander's spe- 

 cies than M. de Vernedil, and his testimony is of much accessory importance in de- 

 termining the real import of the genus Plectambonites. That he himself did not 

 adopt the generic term, is due to the fact that he followed the prevailing custom 

 of rendering to a genus the full breadth of meaning given to it by its author. 



The elongate-lobate muscular scars, and the peculiar structure of the cardi- 

 nal process are features which at once distinguish Plectambonites from allied 

 genera. The former character is sometimes approached in certain species of 

 Rafinesqoina. Species of this genus have probably not appeared earlier than 

 the faunas of the Trenton and Caradoc-Bala * 



The genus disappears in the Niagara ; P. transversalis being the last survivor 

 represented. It has been quite generally believed that the genus reappeared 

 in the Trias and Jura, but many of these species have already proven to be of 

 a distinct type of structure, and all of them will unquestionably be found to 

 differ essentially from PLECTAMBONiTES.f 



Genus CHRISTIANIA,t gen. nov. 



I'LATE XV, FIGS. :i2, 3a; AND PLATK XVa, FIG. 36. 



1837. Plectanibonitex, Pander. Beiti-. zur Geognosie d. i-uss. Reiches, yi. 92, pi. xix, fig-s. 9, 10. 



1840. Orthis, von Eichwald. Ueber <laa Silur. Schicht. Syst. in Estlaiid, p. 148. 



184.">. LeptCRna, db Vernecil. Geol. de la Russ. et des Mont, de TOui-al, p. 228, pi. xv, fig. 2. 



1840. Procluctius, McCoy. Synopsis Silurian Fossils of Ireland, p. 25, pi. iii, fig. 4. 



1853. Leptmna, Davidson. Introd. British Fossil Bi-acliiopoda, pi. viii, figs. 184, 185. 



1871. Leptmna, Davidson. British Silurian Bi-achiopoda, p. 326, pi. xlvii, tigs. 7-lS. 



1S83. LeptWJta, David.son. British Silurian Brachiopoda, Suppl., p. 168, pi. xii, figs. 17-21. 



1883. LeptmiM, Half,. Rept. N. Y. State Geologist for 1882, Exp), pi. xv (46), figs. 32, 33. 



Diagnosis. Shells usually longitudinally elongated, sometimes semielliptical in 

 outline ; normally concavo-convex. Surface smooth or covered with fine radiat- 



ete applirpie par M. Eichwald a une Orthis <\e I'Esthonie. Parmi les Plectambonites de M. Pandei', il y en a 

 ipiatre ipii out une extreme ressemblence aux Tespfece dont nous nous occupons Les Plectambonites planis- 

 siina et crassa sont ceux que nous aurions voulu choisir comme types, mais ces ileux noms ayaiit deja 6te 

 donnes a des Ort?iis on a des Atrypa, nous preferons adopter le nom de coiivexa qui n'a pas encore ete em- 

 ploye." 



*The species LeptWiia sordida and L. decipiens, described l>y Mr. Hillixus, from the Levis formation, 

 prove to be generically distinct, and are discussed under the genus Lei'tella. 



t See the more recent determinations by Munikr de Chalmas, Bittneh, Zuomatek, and others. The 

 fir.st of those authors lia-s established the genera Kdni.N'okeli.a (type. LeptWna Hasina, Bouchard) and Cad- 

 OMBi.LA (type, LeptwiM Mnoiei, Davidson), for some of the Lia.ssir species. 



I This name is proposed as an expression of regard for the memory of Dr. Chrlstian Hei.mucii Pander. 



