OBOLID^. 441 



In the first-mentioned specimen, the entire posterior part is broken off, so that the long-drawn-out elliptic places of 

 attachment (immediately in front of the foot of the broken-off platform) are visible. The second specimen had to be 

 figured from a front \aew, to make the covered places of attachment -^dsible. Between the places of attachment of the 

 central muscles (which in 0. antiquusimus lie nearer one another than with the other species) the slightly developed 

 but distinctly visible median swelling comes in and is produced in the known manner as far as between the places of 

 attachment of the anterior lateral muscle, which are also moved considerably toward the posterior. 



Formation and locality." — Passage beds between the Upper Cambrian and the Ordovician: "Glauconite 

 limestone " at the following locahties: (3961) At Fall, 15 miles (24 km.) west of Reval; (396d) (^ -at Domglint, in Reval; 

 (3961i) at Tischer, iO miles (16 km.) west of Reval; (396]) at Nommeweske, near Palms; (337h [Eichwald, 1860, 

 p. 929]) Orthoceratite limestone near Reval; and (396o) in the entire western part of the east Baltic region; all in the 

 Government of Esthonia, Russia. 



(396k) "Glauconite limestone" at Iswos on the Wolchow; (396z) limestone in the vicinity of Zarskoe Selo; (395w) 

 chlorite-bearing sands in the limestone beds at Pawlowsk, near St. Petersburg; (336e) Orthoceratite limestone at Pul- 

 kowa, near St. Petersburg; and (3961) "glauconite limestone" at Pulkowa, near St. Petersburg; all in the Government 

 of St. Petersburg, Russia. 



(396m) "Lower lenticular layer" of the "glauconite limestone" at Saggad, east of Palms; (396n) white limestone 

 between the "glauconite limestone" proper and the sandy representatives of the "Vaginatum limestone," at Leppiko, 

 near Leetz, on the eastern side of the Baltischport Peninsula, about 25 miles (40.3 km.) west of Reval; (396g) 

 upper limestone at Reval; (396x) chlorite-bearing sands in the limestone beds at Baltischport, about 30 miles (48 km.) 

 west of Reval; (396y) chlorite-bearing sands in the limestone beds at Reval; (336d) Orthoceratite limestone at Reval; 

 and (396p) strata between the "lower lenticular layer" and the "Vaginatum limestone" proper, at Nommeweske, near 

 Palms; all in the Government of Esthonia, Russia. 



(386b) Drift blocks of "glauconite limestone" near Wehlau, 30 miles (48 km.) east of Konigsberg, East Prussia, 

 Germany. 



Obolus (Acritis?) rugatus Walcott. 



Plate XIII, figure 2. 

 Oholus {Acritis'?) rugatus Walcott, 1901, Proc. U. S. Nat. Mus., vol. 23, p. 694. (Characterized as a new species.) 



The concentric surface lines which are the cliaracteristic feature of this shell, although 

 much coarser, are the same type as those of 0. {Acritis) antiquissimus (Eichwald) and terminate 

 on the posterolateral margins m muclt the same manner. It is a very rare form, only one 

 specimen having been collected, although the beds in wliich it occurs were very thoroughly 

 searched during the survey of the Eureka mining district. All that is known of the species is 

 shown by the figure illustrating it. It is probably not an Acritis and probably not an Oholus. 

 The peculiar surface, as shown in Plate XIII, figure 2, is very much like that of a Silurian species 

 named by Clarke Glossina acer} 



This form owes its specific name to the coarseness of the concentric surface lines. 



Formation and locality. — Middle Cambrian: (58) Shaly limestone in upper beds of Secret Canyon shale, east 

 side of New York and Secret canyons, Eureka district [Hague, 1892, Atlas], Eureka County, Nevada. 



SCHMIDTIA Volborth.c subgenus of OBOLUS. 



Schmidtia Volborth, 1860; see Marshall's Nomenclator Zoologicus, p. 137. 

 Not Schmidtia Balsamo-Crivelli, 1863. (Proposed for a genus of Porifera.) 

 Schmidtia Volborth, 1869, Verhandl. Russ.-kais. min. Gesell. St. Petersbm-g, 2d ser., Bd. 4, pp. 208-209. (Discussed 



in German.) 

 Schmidtia Volborth, Dall, 1877, Bull. U. S. Nat. Mus. No. 8, p. 62. (Notes on use of generic name Schmidtia). 

 Schmidtia Volborth, Zittel, 1880, Handbuch der Palseontologie, Bd. 1, Abth. 1, p. 665. (Described in German.) 

 Schmidtia Volborth, Oehlert, 1887, Manuel de conchyliologie, by Fischer, p. 1263. (Described in French.) 

 Schmidtia Volborth, Hall and Clarke, 1892, Eleventh Ann. Rept. State Geologist New York for 1891, p. 244. 



(Described.) 

 Schmidtia Volborth, Hall and Clarke, 1892, Forty-fifth Ann. Rept. New York State Museum for 1891, p. 560. (Copy 



of preceding reference.) 



1 Locality 396d is represented in the collections of the United States National Museum. With the exception of Locality 337h the remaining 

 localities are cited from Mickwitz [1890, p. 213]. 



b Clarke, J. M., New York State Museum, Memoir 9, 1908, pp. 214-215, PI. XLVII, flgs. 7 and 8. 



c The sjTionjTny for this subgenus does not give a complete record of the various genera under which the species now included in Schmidtia 

 were formerly placed: it gives only those references in which the genus is discussed or described. To complete the record the following mere generic 

 references are listed: 



t/njuZa Pander [1830, p. 59]. i OMms Wiman [1902, pp. 62 and 63]. 



Obolus {LingulelU) Walcott [1898b, PI. XXVI, Obolus Moberg and Segerberg [1906, p. 05). 



figs, land 2]. I OioZM Westergird [1909, p. 56]. 



