80 
PALAEONTOLOGY OF NEW YORK. 
A number of genera having more or less 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, Eichwald. 1829. 
1829. Obolus, Eichwald. Zoologia specialis, vol. i, p. 274. 
1830. Ungula, Pander. Beitr. zur Geogn. des Russisch. Reiches., p. 55. 
1840. Orthm Yon Buch. Beitr. zur Bestimmung der Gebirgsform. Russlands. 
1847. Aulonotreta, Kutorga (partim). Ueber die Siphonotretaese, p, 278. 
1848. Dngulites, Bronn. Index Palaeontologicus, vol. iii, p. 1342. 
1871. Ungnlites, Quenstedt. Petrifactenk. Deutschl. Braehiopoden, p. 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 groove on 
the brachial valve is sometimes obsolescent. 
The interior of 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 
* Kutorga and Davidson (Introd. Brit. Foss. Brach., pi. x, figs. 280-285) have not agreed in the determ¬ 
ination of the valves of Obolus. Of Kutorga’s figures of Aulonotreta polita (= Obolus Apollinis), those 
lettered 107), b', c and d (op. cit., pi. vii), are considered by the author as interiors of the dorsal (brachial) 
valve, and figure e, that of the ventral (pedicle-) valve. Davidson considered, and with excellent reason, 
figs. 10 b and b' as dorsal and c, d and e as ventral valves. 
Obolus Apollinis. 
Fig. 33. Pedicle-valve. After Davidson. 
Fig. 34. Brachial valve. After Kutorga. 
