| 180 BRITISH SILURJAN BRACHIOPODA. 
New York State, America; all in beds corresponding with our Wenlock Limestone and 
Shale. 
RayncnonetLaA Lewis, Dav. Pl. XXIII, figs. 25—28. 
TereBRATULA LewisiI, Dav. Bull. Soc. Géol. France, 2nd ser., vol. v, p. 330, pl. iii, 
fig. 30, 1848. 
HeEmiTHyris — MCoy. British Pal. Foss., p. 203, 1852. 
RHYNCHONELLA — _ Salter, Siluria, 2nd ed., p. 250, fig. 57, 2, 1859. 
_— —  Lindstrim. Gottlands Brachiopod., p. 366, 1860. 
Spec. Char. Subrhomboidal or transversely oval ; ventral valve rather less convex than 
the dorsal one ; beak small, acute, much incurved ; sinus rather deep, of moderate breadth, 
sides almost perpendicular ; dorsal valve more or less convex, sometimes gibbous, evenly 
tumid near the beaks, mesial fold rather narrow, prominent, and rounded, rising 
abruptly from the lateral portions of the shell, so that it presents a somewhat pinched 
appearance. Surface of each valve ornamented with from twenty to twenty-six simple 
radiating ribs, of which from two to five occupy the fold, and from one to four the sinus ; 
the surface is also crossed by many projecting, scale-like, concentric ridges, which become 
larger and more numerous as they approach the margin of the shell. Two specimens 
measured— 
Length 8, width 10, depth 5 lines. 
pugoper;,, SLO; Sel ATeee 
Obs. This species is easily distinguished from other British Silurian Riynchonelle 
by its shape and the scale-like concentric laminze which ornament its surface; the mesial 
fold has also often a peculiarly pinched-in appearance, which is best seen from the front, 
as represented in fig. 25a. Like all its congeners, it varies considerably in the number 
and strength of its ribs. When quite young it is much compressed, the fold and sinus 
being scarcely developed. As correctly remarked by Prof. M‘Coy, RA. Lewis is 
quite distinct from &/. (Atrypa) increbescens, Hall, although some depressed varieties 
of the last-named species bear a certain resemblance to the shell under description. Some 
incomplete interiors may be seen in the Woodwardian Museum, Cambridge ; and Prof. 
M‘Coy states that casts show in the ventral valve two short, slightly diverging slits of 
dental lamella, between which are three or four diverging ridges in the rostral portion ; 
and that the dorsal valve shows a wide mesial slit of the thick septa, and impressions 
of two short cardinal teeth just within the ends of the dental lamella of the opposite 
valve. 
Position and Locality. In ‘ Siluria’ (p. 545) the range of this species is said to be in the 
Llandovery and Wenlock. I am, however, acquainted with the shell only from the last- 
named formation, in which at some localities it is exceedingly abundant. I found it at 
