BRACHIOPODA. 
185 
impressions are usually strongly developed, there being beneath the deltidial 
plates a deep scar of the pedicle-muscle, while the adductor impression on the 
pedicle-valve is often very marked. The adductors of the brachial valve and 
the diductors of the pedicle-valve are more or less distinctly defined. 
Shells possessing the features indicated became prevalent in the fauna of the 
Hudson River group {R. capax, Conrad, R. increbescens, Hall, R. dentata, Hall), 
but probably made their earliest appearance in that of the Trenton limestone 
{R. increbescens. Hall, Trematospira quadriplicata, Miller). There is thus far no 
satisfactory evidence of its existence in later faunas. 
Genus R H Y N C H 0 T R E T A, Hall. 1879. 
PLATE LVI. 
1828. Terebratula, Dalman. Kong. Vetenskaps-Akad. Handlingar, p. 141, pi. vi, fig. 3. 
1828. Tei'ebratula, Hisinger. Bidrag till Svei'iges Geognosi, pt. iv, p. 239, pi. vi, fig. 3. 
1839. Terebratula, J. db C. Sowerby. Silurian System, p. 625, pi. xii, fig. 13. 
1846. Atrypa, McCoy. Synopsis Silurian Fossils Ireland, p. 39. 
1848. Hypothyris, Phillips and Salter. Mem. Geol. Survey of Great Britain, vol. ii, pt. i, p. 280. 
1852. Atrypa, Hall. Palaeontology of New York, vol. ii, p. 276, pi. Ivii, figs. 4 a-r. 
1859. Rhynchonella, Hall. Twelfth Ann. Kept. N. Y. State Cab. Nat. Hist., p. 77. 
1859. Retzia, Salter. Murchison’s Siluria, second edition, pi. xxii, fig. 8. 
1860. Rhynchonella, Lindstrom. Ofvers. Kongl. Vetenskaps-Akad. ForhWndl., p. 365. 
1867. Rhyyichonella, Davidson. British Silurian Brachiopoda, p. 164, pi. xxi, figs. 7-11. 
1879. Rhynchotreta, Hall. Twenty-eighth Ann. Kept. N.Y. State Mus. Nat. Hist., pp. 166-168, figs.1-4, 
pi. XXV, figs. 29-38. 
1882. Rhynchotreta, Hall. Eleventh Ann. Kept. State Geologist of Indiana, pp. 309-311, figs. 1-4, 
pi. XXV, figs. 29-38. 
1883. Rhynchonella, Davidson. British Silurian Brachiopoda, Suppl., p. 154, pi. x, figs. 9, 10. 
1889. Rhynchotreta, Beecher and Clarke. Mem. N. Y. State Mus., vol. i. No. 1, iip. 47-51, pi. iv, 
figs. 12-22. 
1889. Rhy7ichotreta, Nettblroth. Kentucky Fossil Shells, pp. 84, 85, pi. xxxii, figs. 58, 59, 62, 63. 
Elongate-triangular, strongly plicated shells with fold and sinus normal, in 
adolescent and mature stages; long and broad cardinal slopes ; beak erect, acu¬ 
minate and produced on the pedicle-valve. Foramen at maturity apical, its upper 
margin encroaching on the substance of the valve. Deltidium very conspicuous, 
convex, the component plates, in their later development, being anchylosed along 
the median suture. Dental lamellae vertical, resting on the bottom of the 
valve and enclosing a deeply impressed muscular scar; diductor scars elongate- 
flabelliform, divided by oblique ridges into anterior and posterior members; 
