OBOLIDiE. 413 



pecuKar interior configuration as described and shown in the illustrations. This species is stated 

 to be very rare and restricted to tlie Oholus sandstone. 



The specific name was given in honor of Dr. Fr. Schmidt. 



Formation and locality. — Tipper Cambrian: (395 [Mickwitz, 1896, p. 153]) Oholus sandstone at Joa, near Jege- 

 lecht, 12 miles (19.3 km.) east of Reval, Government of Esthonia, Russia. 



^ Obolus selwyni (Matthew). 



Plate XXXVI, figures 1, la-h, 2, 2a-b; Plate XXXVII, figures 1, la-f. 



Lingulella selwyni Matthew, 1895, Trans. Roy. Soc. Canada for 1895, 2d ser., vol. 1, sec. 4, No. 13, pp. 255-256, PI. 

 I, figs. la-b. (Described and discussed as a new species. The specimen represented by fig. lb is redrawn in 

 this monograph, PL XXXVII, fig. Ic.) 



Obolus xquiputeis Matthew, 1902, idem, 2d ser., vol. 8, sec. 4, No. 3, p. 94, PI. I, figs. 4a-e. (Characterized. The 

 specimens represented by figures 4b and 4d are redrawn in this monograph, PI. XXXVI, figs. 2 and 2a, re- 

 spectively.) ' 



Lingulella selwyni Matthew, 1903, Geol. Survey Canada, Rept. Cambrian Rocks Cape Breton, pp. 62-63. (Notes on 

 orientation of shells.) 



Lingulella selwyni Matthew, 1903, idem, pp. 116-123, figures on p. 117, and PI. VII, figs. la-c. (Described and dis- 

 cussed. The original reference, Matthew, 1895, pp. 255-256, is copied on pp. 120 and 121. The figures given 

 on p. 117 are diagrammatic drawings based on the specimens figured by Matthew, 1895, PI. I, figs, la and lb. 

 Matthew's original drawings are, however, also copied in this reference, Matthew, 1903, PI. VII, figs, la and 

 lb. PI. XXXVII, fig. Ic, of this monograph represents the specimen upon which Matthew based the diagram- 

 matic figures given in the right-hand figure on p. 117 and that given in PI. VII, fig. lb. PI. XXXVI, figs. 1 

 and Ic, of this monograph represent the specimens on which Matthew based the diagrammatic figures given in 

 the left-hand figure on p. 117 and that given in PL VII, -figs, la and Ic.) 



Oholus xquiputeis Matthew, 1903, idem, p. 139, PL VIII, figs. 2a-e. (Described as a new species, but it is not the 

 first reference to the species ; see above. The marginal reference gives the species as Oholus {Eooholus) xquiputeis. 

 Figs. 2a-e are copied from Matthew, 1902, PL I, figs. 4a-e.) 



General form subovate, broadly rounded in front. Ventral valve subacuminate and dorsal 

 valve broadly rounded at the beak. Surface of the shell marked by very fine, concentric striae 

 and lines of growth and indistinct very narrow imdulations of the shell radiating from the beak. 

 Wlien the thin exterior shell is exfoliated fine radiating lines are seen, and the inner surface 

 (outside of the visceral areas) shows radiating lines toward the anterior margin and irregularly 

 distributed punctse. The shell is of rather more than medium thickness. It is built up of a 

 thin outer layer and several inner layers, very much as the shell of Lingulella acutangula (Roemer) 

 (PL XVII, figs. Im, In, and lo). 



A large, slightly distorted ventral valve has a length of 14 mm.; width, 11 mm. The origi- 

 nal proportion of length and width of this specimen was probably 14 to 12. The dorsal valve 

 was probably of equal length and width. 



The area of the ventral valve is more or less distorted in all the specimens; its character is 

 best shown in Plate XXXVII, figure lb; and the area of the dorsal valve in Plate XXXVII, 

 figure le. The pedicle furrow is strong and well defined (PI. XXXVII, fig. lb). 



The cast of the interior of the ventral valve shows the visceral cavity and the heart-shaped 

 pit (x) (PI. XXXVII, fig. 1 d) so characteristic of Obolus. There are no traces of a median septum 

 in the ventral valve; in the dorsal valve it is a sharp, narrow ridge (PI. XXXVI, figs. le-g). 



The muscle scars of the valves are well shown in casts of the interior. The umbonal scar of 

 the dorsal valve is elongate (PL XXXVII, figs. Ic and If, and PL XXXVI, fig. le). I have not 

 observed it in the ventral valve. The scars of the central muscles (h) are distinct in the dorsal 

 valve (PL XXXVII, fig. Ic), but on the ventral" valve they are merged with the middle laterals 

 in the trapezoidal area (c) (fig. Id). The outside laterals (1) are preserved in interiors of the 

 ventral valve (PL XXXVI, figs. Id and le) and the dorsal valve (PL XXXVI, fig. le). The 

 middle laterals (k) are shown on the dorsal valve (PL XXXVI, fig. le), but have not been seen 

 on the ventral valve. The anterior laterals are shown for the dorsal valve at (j) (fig. Ic). The 

 transmedian scars (i) are preserved on casts of the dorsal valve (PL XXXVII, figs. Ic, le, 

 and If) and the ventral valve (PL XXXVI, fig. la). 



