﻿94 



BRITISH CARBONIFEROUS BRACHIOPODA. 



Terebratula acuminata, Phillips. Geology of Yorkshire, vol. ii, p. 222, pi. xii, figs. 



4—9, 1836. 



— mesogonia. Ibid., pi. xii, figs. 10 — 12. 



— acuminata, Be KonincJc. Animaux fossiles de la Belgique, p. 278, pi. xvii, 



fig. 3, a, b, c, d,f (not the other figures), 1843. 

 Atrypa acuminata, M'Coy. Synopsis of the Characters of the Carboniferous Fossils of 

 Ireland, p. 151 ; also woodcut, fig. 32, 1844. 

 — — UOrbigny. Prodrome de Paleontologie Stratigraphique, vol. i, p. 



146, 1849. 



Rhynchonella acuminata, Morris. A Catalogue of British Fossils, p. 146, 1854. 

 Hemithyris — M'Coy. British Palaeozoic Fossils, p. 381, 1858. 



Spec. Char. Very variable in shape and character; more or less trigonal, heart-shaped, 

 or obscurely pentagonal ; generally wider than long. Dorsal valve convex, often gibbous, 

 and much elevated at its frontal margin, the lateral portions sloping rapidly on either side ; 

 a distinct mesial fold is rarely perceptible. Beak in ventral valve small, incurved ; foramen 

 minute, situated under the extremity of the beak, and margined by a deltidium. Sinus 

 either concave or angular, of great width, and of variable depth ; originating at a short 

 distance from the extremity of the beak, it extends to the front, where it forms either a 

 regular curve or is prolonged in the shape of an acute cuneiform extremity. Externally 

 the surface is smooth, finely striated, or more or less strongly plaited. 



Ventral aspect. Umbonal aspect. 



Rk. acuminata, internal casts. 



k. Adductor, or occlusor. R. Cardinal, or divaricator. p. Pedicle, or ventral adjustor, muscular impres- 

 sions, v. Vascular markings, o. Ovarian spaces. 



In the interior of the dorsal valve the hinge-plate is divided, and to these are attached 

 a pair of short, curved, shelly processes, for the support of the oral arms. On the bottom of 

 the valve may be seen the quadruple impressions produced by the adductor or posterior 

 and anterior occlusor muscle of Hancock ; and in the ventral valve the adductor (or 

 occlusor), cardinal (or divaricator), and pedicle (or ventral adjustor) muscular scars may 

 be distinctly traced. The ovarian and vascular spaces and impressions are also clearly 

 defined in the interior of both valves. Dimensions very variable ; four examples have offered 

 the following proportions : 



