298 PALEONTOLOGY OF NEW YORK. 



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

 cies than M. de Verneuil, 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 

 Rafinesquina. 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. 



PLATE XV, FIGS. 33, 33; and PLATE XVa, FIG. 36. 



1887. Plectambonites, Pander. Beitr. ziii' Geognosie d. i-uss. Reiches, p. 92, pi. xix, tigs. 9, 10. 



1840. Orthis, von Eichwald. Ueber das Sikir. Schioht. Syst. in Estland, p. 148. 



1845. LeptcBna, de Vernedil. Geol. de la Russ. et des Mont, de rOural, p. 228, pi. xv, fig. 2. 



1846. Productus, McCoy. Synopsis Silurian Fossils of Ireland, p. 25, pi. iii, fig. 4. 

 1853. Leptmna, Davidson. Introd. Bi-itish Fossil Brachiopoda, pi. viii, figs. 184, 185. 

 1871. 'Leptwna, Davidson. British Silnrian Bi-achiopoda, p. 326, pi. xlvii, figs. 7-18. 

 1883. Leptmna, Davidson. British ^ilurian Brachioi^oda, Suppl., p. 168, pi. xii, figs. 17-21. 

 1883. Leptcena, Hall. Rept. N. Y. State Geologist for 1882, Expl. 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 applique par M. Eichwald a une Orthis de I'Esthonie. Pai-mi les Plectambonites de M. Pandei', 11 y en a 

 quatre qui ont une extreme I'essemblence aux I'espece dont nous nous occupons- Les Plectambonites plants- 

 sima et crassa sont ceux que nous anrions vouki choisir conime types, mais ces deux noms ayaiit deja 6te 

 donnes a des Orthis ou a des Atrypa, nous prefei'ons adopter le nom de convexa qui n'a pas encore ete em- 

 ploye." 



*The species Leptwna sordida and L. decipieiis, described by Mr. Billings, from the Levis formation, 

 prove to be generically distinct, and ai'e discussed under the genus Leptella. 



t See the more recent determinations by Muniee de Chalmas, Bittner, Zugmayer, and others. The 

 first of these authors ha-s established the genera Koninckella (type. LeptCRna liasina, Bouchard) and Cad- 

 OMBLLA (type, Leptmna Moorei, Davidson), for some of the Liassic species. 



I This name is pi-oposed as an expression of regard for the memory of Dr. Christian Heinrich Pander. 



