80 PALAEONTOLOGY OF NEW YORK. 



A NUMBER OF GENERA having morc or less close relationship to Obolella have 

 been described by European writers, but are not at present known to have 

 representatives in American founas. Such are Obolus, Monobolina, Spoxdy- 

 LOBOLUS, AcRiTis, ScHMiDTiA, MiCKWiTZiA and Neobolus. The original specimens 

 of these genera are mainly from primordial faunas, but they are to a great 

 degree imperfectly known, the figures and descriptions given by various authors 

 not always serving the requirements of the present status in the investigation 

 of these fossils. Much has yet to be learned in regard to the internal charac- 

 ters of most of tliem before their generic position can be established. 



OBOLUS, EicHWALD. 1829. 



1S29. Obohis, EiCHWALD. Zoologia sperialis. vol. i, p. 27i. 



1830. Ungula, Pander. Beitr. zni- Geogn. des Russisch. Ri-iches., p. 55. 



1840. Oi-tliU, VoN Bdcb. Beitr. zur Beslimmung: <ler Gebii-gsform. Russlamis. 



1847. Aulonotreta, Kdtorga (partiin). Ueber die Siphonotretsese, p, 278. 



J848. Viigulites, Bronn. Index Palaeontologicus, vol. iii, p. 1342. 



1871. Uii^ulHfii. QuEN.STEnT. Petrifaclenk. Deutschl. Brachiopodeii, p. 671. 



Type, Obolm Apollinis, Eichwald. Unguliten-schichten. 



This is the best known and most thoroughly studied of all the genera above 

 named. Externally the shells are much like those of Obolella, but are 

 generally larger and somewhat tlatter. The a\ 



valves are unarticulated, both having broad, i, 



grooved cardinal areas, though the groove on C "S '^ 

 the brachial valve is sometimes obsolescent. 

 The interior of the pedicle-valve* shows a oboius Apoinms. 



pair of well-defined cardinal or posterior ^J^^l '^^^:;t^,''lZrZ'ro^t. 

 adductor impressions, just behind the cardinal area and separated by a more or 

 less developed median septum extending to about the center of the valve. 

 The "laterals" are well developed and occupy a position not equivalent to the 



* KuTOROA and Davidsox (Iiitrod. Bi-it. Foss. Bracli., i)l. x, dgs. 280-285) have not agreed in the deterin- 

 iuatioii of the valves of Obolus. Of Kutohga's tiH'i"'es of Auloiwtnta polita (= Oholns Apollinis), those 

 lettered 10 6, b', c and d {<>]). cit., pi. vii), are considereil by the author as interiors of the (Uirsal (brachial) 

 valve, and figure t; that of the ventral (pedicle-) valve. Davidson considered, and with excellent reason, 

 figs. 106 and 1/ jis dorsal and c, d and e as ventral valves. 



