OBOLID^. 555 



outer surface, especially over the anterioi- and lateral portions of the shell, where they are 

 much more numerous. In many specimens the shell substance has been replaced by calcite. 



Interiors of the ventral valve show considerable difference in the position of the main 

 vascular sinuses. They are usually well out toward the sides. In the dorsal valve the main 

 vascular sinuses are widely separated, and the visceral area is well extended toward the 

 front. 



Observations. — ^Wlien studying the collections made by S. Ward Loper on McLean Brook 

 in 1900, 1 identified the shells now placed under Lingulella (Lingulepis) exigua a,s "Obolus {Lin- 

 gulepis) gregwa." But at that time I had only the somewhat imperfect material in Matthew's 

 collection from Dugald Brook for the purposes of comparison. With a large series of well- 

 preserved specimens collected on Dugald Brook in 1901 by Loper, the fact that the two species 

 had been confused became at once apparent. Lingulella {Lingulepis) gregwa is found in great 

 numbers at a lower stratigraphic horizon beneath the Paradoxides zone, wliile L. (L.) exigua 

 occurs at the summit of the Middle Cambrian fauna in association with Paradoxides. Both 

 species have strong points of resemblance to L. (L.) acuminata (Conrad) and both, in their 

 younger stages, depart to such an extent from the typical forms of the adult shell that they 

 might be considered a distinct species if found at another locality or stratigrapliic horizon. 



The specific name is derived from Gregwa Brook, on wliich specimens of the species occur. 



Formation and locality. — Middle Cambrian: (lOp) Sandstone just below the waterfall in Division E2b of 

 Matthew's [1903, p. 21] Etcheminian, on Dugald Brook, Indian River; (lOp') sandstone one-fourth mile (0.4 km.) 

 from lower bridge, on Gregwa Brook, Indian River; (lOp'') sandstone on the small brook on the hill between the 

 bridge over Indian River and McPhees Brook; (13t") sandstones of Divisions Elc and Eld of Matthew's [1903, p. 21] 

 Etcheminian, on Dugald Brook, Indian River; (344e [Matthew, 1903, p. 78]) shales of Division Eld of Matthew's 

 [1903, pp. 28 and 29] Etcheminian, on Boundary Brook, eastern side of the Escasonie Indian Reservation; (344ka 

 [Matthew, 1903, p. 77]) sandstones of Division Elb of Matthew's [1903, p. 21] Etcheminian, on Dugald Brook, Indian 

 River; (344m [Matthew, ,1903, p. 78]) sandy shales of Division Eld of Matthew's [1903, -p. SI] Etcheminian, on Dugald 

 ■ Brook, Indian River; and (344n [Matthew, 1903, p. 33]) shales in the gorge at the old mill on McCodrum Brook, Mira 

 River; all in eastern Cape Breton, Nova Scotia. 



Lingulella (Lingxjlepis) geegwa robusta (Matthew). 



Idngulepis gregwa robusta Matthew, 1903, Geol. Survey Canada, Rept. Cambrian Rocks Cape Breton, p. 57. (Notes 



on orientation of shells.) 

 Lingulepis gregwa robusta Matthew, 1903, idem, p. 131. (Characterized as a new variety.) 



Matthew separates a form with a thicker sheU and straighter cardinal margins as the 

 variety robusta. My impression is that these characters are so largely the result of the con- 

 dition of preservation of the specimens in the matrix that the variety has very little value. 



Formation and locality. — Middle Cambrian : (lOp) Sandstone just below the waterfall in Division E2b of Matthew's 

 [1903, p. 21] Etcheminian, on Dugald Brook, Indian River; (lOp') sandstone one-fourth mile (0.4 km.) from lower 

 bridge, on Gregwa Brook, Indian River; (lOp") sandstone on the small brook on the hill between the bridge over 

 Indian River and McPhees Brook; (13t") sandstones of Divisions Elc and Eld of Matthew's [1903, p. 21] Etche- 

 minian, on Dugald Brook, Indian River; (344h [Matthew, 1903, p. 79]) sandy layers in the shales of Division Ele of 

 Matthew's [1903, p. 21] Etcheminian, on Dugald Brook, Indian River; and (344m [Matthew, 1903, p. 78]) sandy shales 

 of Division Eld of Matthew's [1903, p. 21] Etcheminian, on Dugald Brook, Indian River; all in eastern Cape Breton, 

 Nova Scotia. 



Lingulella (Lingulepis) longinervis (Matthew). 



Plate XLIV, figures 2, 2a-g. 



Lingulepis longinervis Matthew, 1903, Geol. Survey Canada, Rept. Cambrian Rocks Cape Breton, pp. 133-135, PI. 

 \ VII, figs. 6a-g. (Described and discussed as a new species. The specimen represented by figure 6f is redrawn 



in this monograph, PI. XLIV, fig. 2e.) 



This species diuers from Lingulella (Lingulepis) gregwa (Matthew) in having the sides of 

 the ventral valve extended in a nearly straight line bej^ond the center of the valve. Some of 

 Matthew's specimens have a concentrically striated surface with only a trace of the character- 

 istic surface of L. (L.) gregwa. Others show more of the ornamented surface, and in specimens 



a Doubtfully identifled from this locality. 



