SYNTROPHIID^. 797 



Type. — Camerella antiqua Billings [1861b, p. 10]. 



The generic name is derived from the town of Swanton, Vermont, near which the type 

 species occurs. 



SWANTONIA ANTIQUATA (BlUings) . 

 Plate CIV, figures 5, 5a-b. 



Camerella antiquata Billings, 1861, Geol. Survey Canada, Paleozoic Fossils, vol. 1, pp. 10-11, fig. 13, p. 10. (De- 

 scribed and discussed as a new species.) 



Camerella antiquata Billings, 1861, Report on the Geology of Vermont, vol. 2, p. 949, fig. 353. (Copy of preceding 

 reference.) 



Camerella antiquata Billings, 1862, Report on the Economic Geology of Vermont, by Hager, p. 221, fig. 353. (Copy 

 of Bilhngs, 1861b, pp. 10-11, and fig. 13.) 



Camerella antiquata Billings, 1863, Geol. Survey Canada, Fifteenth Rept. Progress, fig. 290, p. 284. (No text refer- 

 ence. Fig. 290 is copied from Billings, 1861b, fig. 13, p. 10.) 

 -Camarella antiquata Billings, Walcott, 1886, Bull. U. S. Geol. Survey No. 30, pp. 122-123, PI. VII, fig. 8. (Original 

 description, Billings, 1861b, pp. 10-11, copied. The specimen represented by fig. 8 is redrawn in this mono- 

 graph, PL CIV, fig. 5.) 

 -Camarella antiquata Billings, Walcott, 1891, Tenth Ann. Rept. U. S. Geol. Survey, p. 613, PL LXXII, fig. 3. (No 

 text reference. Fig. 3 is copied from fig. 8 of the preceding reference.) 



Camarella ? antiquata Billings, Hall and Clakkb, 1893, Nat. Hist. New York, Paleontology, vol. 8, pt. 2, pp. 220-221. 

 (Mentioned in discussion of genus Camarella.) 



Protorhyncha f antiquata (Billings), Schuchekt, 1897, Bull. U. S. Geol. Survey No. 87, p. 334. (Merely changes generic 

 reference.) 



Swantonia antiquata (Billings), Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, pp. 296-297. (Described and discussed 

 as below.) 



Ventral valve ovate, moderately convex; apex pointed and incurved over the area nearly 

 to the plane of the margins of the valve; surface marked by from 8 to 12 or more rounded 

 ribs that extend back well toward the apex; a slight flattening of the median portion suggests 

 that a shallow median sinus may be found on old shells. The shell illustrated has a length 

 and width of 11 mm. 



A cast of the interior of a ventral valve shows no traces of muscle scars or vascular mark- 

 ings; two strong teeth are indicated, also a narrow, strong, concave shelf or area; the area or 

 shelf is free from contact with the bottom of the valve, a recess or chamber existing beneath it. 



Observations. — The area or shelf may be considered as a short, free spondylium, corre- 

 sponding to the short spondylium of Camarella volhorthi Billings as illustrated by Hall and 

 Clarke [1892c, PL LXII, fig. 18]. Swantonia is closely related to Camarella, but it differs in 

 the absence of a supporting median septum beneath the spondylium of the ventral valve. 

 No specimens of the dorsal valve have been observed. 



Formation and locality. — lower Cambrian: (319e)<» Sandy shales 2 miles (3.2 km.) east of Swanton, Franklin 

 County, Vermont. 



Swantonia weeksi Walcott. 



Plate CIV, figure 6. 



Swantonia weehsi Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, p. 297. (Characterized as below as a new species.) 



This shell has the general form of Swantonia antiquata (Billings), but the ribs are finer, 

 more numerous, and crossed by fine, sharp, concentric strise. Only the exterior of the ventral 

 valve appears to be represented in the collection made by Mi\ F. B. Weeks. 



Formation and locality. — lower Cambrian : (Iv) Shales of No. 3 of the Silver Peak group, Barrel Spring 

 section [Walcott, 1908f, p. 189], 3 miles (4.8 km.) north of Valcalda Spring and 4 miles (6.4 km.) west-northwest of the 

 Drinkwater mine. Silver Peak quadrangle (U. S. Geol. Survey), Esmeralda County, Nevada. 



o Billings [1861b, p. 11] gives the locality as 1.5 miles (2.4 km.) east of Swanton, Vermont. 



