ACROTRETID^. 695 



over the false area. All that is known of it is represented by the illustrations (PI. LXVII, 

 figs. 3, 3a-d). 



The varietal name is derived from the Teton Mountains, Wyoming. 



Formation and locality. — Middle Cambrian: (4e) Limestones about 950 feet (289.6 m.) above the uncon- 

 formable base of the Cambrian in the divide at the head of Jackson Creek (locally known as Sheep Creek), a creek 

 flowing into Jackson Lake about 0.5 mile (0.8 km.) south of its northwestern corner, Teton Mountains, Grand Teton 

 quadrangle (U. S. Geol. Survey), Uinta County, Wyoming. 



AcEOTEETA? MINIMA (Barraude). 

 Plate LXXVII, figures 7, 7a. 



Obolus? TninimuB Bakrande, 1879, SystSme silurien du centre de la Bohgme, vol. 5, pt. 1, PL XCV, figs, ii: 1-5. 

 (Not described, but figured as a new species. Figs. 3A and lA are reproduced in this monograph, PI. LXXVII, 

 figs. 7 and 7a, respectively.) 



This minute shell may possibly belong with Acroihele, but with the data furnished by 

 the illustrations of Barrande [1879b, PI. XCV, figs. ii:l-5] a provisional reference is made 

 to Acrotreta. It certainly is not an Oiolus. The figures illustrate all the characters known. 



Formation and locality. — Lower Ordovician: (303d [Barrande, 1879b, PI. XCV]) Etage dl, Swarow, Bohemia, 

 Austria-Hungary . 



AcEOTEETA MISEEA (Billings). 



'^ Plate LXXII, figures 2, 2a-l. 



Obolellaf miser Billings, 1872, Canadian Naturalist, 2d ser., vol. 6, No. 4, pp. 470-471. (Described and discussed.) 



Oholella f miser Billings, 1874, Geol. Survey Canada, Paleozoic Fossils, vol. 2, pt. 1, p. 69. (Copy of preceding refer- 

 ence.) 



Idnnarssonia misera (Billings), Matthew, 1886, Trans. Roy. Soc. Canada for 1885, 1st ser., vol. 3, sec. 4, No. 4, 

 pp. 35-36, PI. V, figs. 12, 12a-e. (Described and discussed.) 



Linnarssonia misera (Billings), Hall and Clarke, 1892, Nat. Hist. New York, Paleontology, vol. 8, pt. 1, pp. 108-109, 

 PL III, figs. 35-37. (Mentioned. Figs. 35 and 36 are drawn from the specimens figured by Matthew, 1886, 

 PL V, figs. 12c and 12, respectively.) 



Acrotreta miser (Billings), Walcott, 1902, Proc. U. S. Nat. Mus., vol. 25, pp. 590-591. (Described essentially as 

 below.) 



The abundant material representing this species that I collected in Newfoundland gives 

 illustrations that present its characters with such fullness and detail that minute description 

 is unnecessary. Plate LXXII, figures 2, 2a-e of the ventral valve, show variation in outline, 

 also of the cast of the apical callosity, cardinal scars, and base of main vascular sinuses. Figures 

 2h-l illustrate the interior of the dorsal valve. 



The outer surface is marked by fine concentric striae and growth lines, and the inner 

 layers or lamellse by very fine radiating strise. The minute pedicle aperture is on the back 

 side of the apex, opening almost posteriorly in some examples. 



This is a small species, averaging from 1.5 to 2.5 mm. in length. 



Formation and locality. — Middle Cambrian: (1 and 2) Shales of zones A and B, respectively, of No. 7 of the 

 Manuels Brook section [Walcott, 1891b, p. 261], Manuels Brook, Conception Bay; (314 [Billings, 1872b, p. 470]) 

 Paradoxides zone on Chappie Arm, Trinity Bay; (314h) shale on Manuels Brook, Conception Bay; (6g) limestone near 

 the base of the Middle Cambrian, northwest side of Chappie Arm Harbor, about 1 mile (1.6 km.) from its head. Trinity 

 Bay; (6h) limestone in the southwest cove of Chappie Arm, Trinity Bay; and (6r) limestone on the west side of 

 Manuels Brook, Conception Bay; all in Newfoundland. 



'(2s and 2t) Shales and interbedded limestones in the upper part of the Paradoxides zone, Hastings Cove [Matthew, 

 1898b, p. 38], on Kennebecasis Bay, 0.5 mile (0.8 km.) northeast of Torryburn, on the Intercolonial Railway, north- 

 east of St. John; and (3011 [Matthew, 1886, p. 36]) shale of Division Id of Matthew, on Porters Brook, St. Martins; 

 both in St. John County, New Brunswick, Canada. 



ACEOTRETA NEBOENSIS Walcott. 



Plate LXXVII, figures 9, 9a-b. 



Acrotreta neboensis Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, pp. 300-301. (Described as below as a new species.) 



Ventral valve moderately elevated, the apex projecting slightly over the nearly vertical false 

 area. The latter is marked midway by a very narrow false pedicle furrow. The transverse 



