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PALAEONTOLOGY OF NEW YORK. 
axial line. The first one-third of this tube is swollen and thickened, but 
thenceforward it passes, with parallel edges, to the anterior margins, where it 
is probably closed, though usually broken. Dorsal valve more depressed, its 
greatest convexity being in the center. Cardinal area as in the opposite valve, 
but narrower. A closed tube, beginning in a swelling just in front of the car¬ 
dinal line, is continued [from the center of the shell] to the anterior margin 
as an open channel. Muscular scars as in Obolus and Helmersenia, but more 
sharply defined.” (Pander, loc. cit.) 
Type, Orbicula Buchi, Yerneuil. 1845. Geol. de la Russ, de l’Europe et des 
mont. d’Oural, p. 288, pi. xix, figs. 1 a, b, c. 
This most peculiar genus presents a close alliance in its muscular impressions 
to Obolus, perhaps more nearly to the Neobolus of Waagen, but in its interior 
closed tubes, that of the pedicle-valve communicating with the external fissure, 
its relationship to the Siphonotretids is demonstrated. Too little is known of 
the permanent characters of the fossil to form any reliable conclusions in regard 
to its proper association, but from the foregoing description it would appear to 
present the anomalous character of a Siphonotretid in which the pedicle-tube 
is in a condition of atrophy, compelling the pedicle to pass between the 
valves, over the cardinal area, as in Obolus. The presence of a caecal tube in 
each valve, if ever devoted to the passage of the pedicle, is altogether un¬ 
precedented. 
In regard to the propriety of the generic term Keyserlingia, it may be 
observed that although Pander’s description and illustration are given without 
specification of the typical species, the genus was founded on the “ Orbicula, 
Murch., Vern„ Keys. Geol. de la Russie, 1845, vol. ii, pag. 288,” i. e., Orbicula 
Buchi, not 0. reversa, Vern., which has been quoted by Dall* as the type-spec¬ 
ies, but which is described on page 289 of that work. The genus Orbicella, 
D’Orbigny, 1847, was evidently founded to include the class of shells for which 
Sharpe, in the same year, proposed the name Trematis. It does not appear, 
however, that any example was cited with the first use of this term in the 
* Bulletin No. 8, U.'S. National Museum, p. 39. 1877. 
