178 PALEONTOLOGY OF NEW YORK. 



upon the apical substance of the valve. Persistence of any of these conditions 

 at maturity may be of collateral value in determining the subdivisions of these 

 fossils, but it is impossible to base important values upon them. It is indeed 

 uncertain whether the authors of the names above mentioned had before them 

 species of Rhynchonella, and those terms must necessarily be rejected. 



The first inquiries before us are : What is Rhynchonella in its strict signi- 

 fication ? and, How far is it represented in palaeozoic faunas ? 



Genus RHYNCHONELLA, sensu stricto. 



PLATE LVI. 



* 1809. Rhynchonella, Fischer de 'Waldheim. Notice des Fossiles du Gmiv. <le Moscou, p. 35, pi. ii, 

 figs. 5, 6. 



1827. Rhynclionella, de Blainville. Diet. de3 Sciences Naturelles, vol. xlv, p. 426. 



1837. Rhynchonella, Fischer de Waldheim. Oi'yctogr. du Gouv. de Moscou, pi. xxiv. 



1853. Rhynchonella, Davidson. Introd. British Fossil Biachiopoda, pi. vii, fig. 99. 



1856. Rhynclionella, Suess. Classif. dei- Bi'achiopoden vou Th. Davidson, pi. iv, tig. 1. 



1871. Rhynchonella, Quenstedt. Petrefactenkunde Deutschland.s ; Brachiopoden, pi. xxxviii, tig. 108. 



ISSO. Rhynchonella, Zittel. Handb. dei- Paliiontologie, \i. 689, figs. 529 a-d. 



Subpyramidal shells having the margins of the valves sinuous or angulated. 

 Pedicle-valve with a median sinus beginning in front of the convex umbo, and 

 in the type-species, becoming broad and deep, producing a prominent lingui- 

 form extension at the anterior margin. Brachial valve convex in the umbonal 

 region and developing anteriorly a prominent median fold. Surface of both 

 valves more or less plicated, often accompanied (as in the type) by fine con- 

 centric lines of ornament. Tlie apex of the pedicle-valve is but slightly 

 incurved and exposes a circular or elongate-oval foramen enclosed by deltidial 

 plates beneath, and above by the substance of the valve. There is a narro-w 

 pseudo-area defined by oblique cardinal ridges diverging from the beak. On 

 the interior the teeth are well developed and are supported by lamellae which 

 rest on the bottom of the valve near the beak, but are free anteriorly. The 

 muscular area consists of a moderately deep oval scar extending one-third the 

 length of the valve, and composed of two large diductors completely enclosing 



*Tlie citations here given refer only to Rhynchonella loxia. Accounts of congeneric Jurassic species 

 will lie found in the works of Davidson, Fischer db Waldheim, Sowerby, d'Archiac and db Vernedil. 



