80 



PALAEONTOLOGY OF NEW YORK. 



A NUMBER OF GENERA having more or k'ss close relationship to Obolella. have 

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

 representatives in American faunas. Such are Obolus, Monoboltna, Spondy- 

 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 them before their generic position can be established. 



OBOLUS, EicHWALu. 1829. 



1S29. Oholus, EicinvALD. Zoologia spetnali!?. vol. i, p. 274. 



1830. Vnrjula, P.\nder. Beitr. znr Geogn. des Russisch. Reiches., p. r)5. 



1840. Ovthii, Von Buch. Beitr. zur Bestimmungr fler Gebirgsform. Russlands. 



1847. Aulonotreta, Kdtorg.\ (partim). Uebei- ilie Siphonotretsea;, p, 27S. 



1848. XJnyulUes, Bronn. Index Palsontologicus, vol. iii, p. 1342. 



1R71. VvsMtes. Qiiknstedt. Petrifactenk. Deiitschl. Brachiopoden, ji. 671. 



Type, Obolus 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 flatter. The 

 valves are unarticulated, both having broad, 

 grooved cardinal areas, though the gi-oove on 

 the brachial valve is sometimes obsolescent. 

 The interior oi' the pedicle-valve* shows a 

 pair of well-defined cardinal or posterior 

 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 



* KuTORG.A and David.so.v (Inti'od. Brit. Foss. Bi-ach., pi. x, fifjs. 280-28ri) have not agreed in the determ- 

 ination of the valves of Obolus. Of Kutohga's lif^-ures of Aahmotrcta poHta (= Oholus Apollinis), those 

 lettered 10 &, h', c and d (op. cit-, pi. vii), are considered by the author as interiors of the dorsal (bi'achial) 

 valve, and fifjure /■, that of the ventral (pedicle-) valve. Davidson considei'ed, and with excellent reason, 

 tigs. 10 fc and b' as dor.'sal and o, d and e an ventral valves. 



Obolus Apollinis. 

 Kiu. 33. rediclevahe. Al'ler DAVIDSON. 

 KiG. 34. Briiclnal valve. After Kutorga. 



