28 BRITISH CRETACEOUS BRACHIOPODA. 



Warminster, where it is very abundant ; but I am not aware of its positively having been 

 found in any other locality, excepting perhaps in the Chloritic Marl of Chard, where the 

 species is, however, very rare. T. pectita is easily distinguished from T. Menardi, from its 

 want of a mesial fold. On the Continent, T. pectita is found at Cap la Heve, near 

 Havre, but we do not know it to occur at Swanage Bay, Dorsetshire, as stated by 

 M. D'Orbigny. 



Plate III, figs. 29-30. Specimens in the Collection of Mr. Cunnington, of Devizes. 



Sub-Genus — Triuonosemus, Komiy. 1825. 



Animal fixed to rocks, or other marine bodies, by a pedicle issuing from the 

 extremity of the beak ; shell inequivalved, irregularly oval, circular, or rhomboidal, as wide 

 as long, or longer than wide ; larger valve always convex ; smaller valve moderately so, flat 

 or longitudinally depressed, beak produced, more or less recurved, and truncated by a small 

 oval elongated foramen, beginning at the summit of the beak, and directing itself on the 

 opposite side to the area. Area large, often nearly as wide as the shell, triangular, flat, 

 edged and carinated exteriorly ; deltideum occupying less than a third of the surface ; a 

 small portion only surrounding the foramen. Surface ornamented by numerous small 

 radiating costae, augmenting by intercalation at variable distances from the beak and umbo. 

 Hinge line very obtuse, sometimes straight ; valves articulating by means of two teeth in 

 larger and corresponding condyles in smaller valve ; between these last, a remarkably 

 developed boss, or cardinal muscular fulcrum is visible, extending in some species 

 considerably beyond the hinge line, and filling a corresponding cavity in the beak of 

 larger valve ; a short, thick, elevated, longitudinal septum, occupies about half of the 

 length of the valve, and on either side of which two deep oval muscular impressions are 

 visible ; apophysary system or loop doubly attached ; the riband-shaped lamella are first 

 fixed to the sides of cardinal muscular fulcrum, and after proceeding to a short distance, 

 are again attached to the highest point of the septum, before bending back on themselves 

 to form the loop. Structure perforated, dimensions variable, the largest specimen known 

 not exceeding 20 lines in length. 1 



Obs. This genus was proposed in 1825 by Kcenig (Icones Fossilium Seciiles) under 

 the following characteristic, " Trigonosemus nob. (Mollusca Brachiopoda) Testa inaequivalvis 

 ovato-rotunda, valvarum altera superne producta in rostrum acuminatum S. truncatum 

 apicse perforatum externe convexum, interne planum; facie plana signo subtriangulari 

 aperturam clausam indicante notata; nomen generis ex rostri signo triangulari. Eig. 73. 

 Trigonosemus elegans." 



1 The largest specimen of this genus I have seen is preserved in the collection of Mr. Morris, obtained 

 in Cretaceous beds near Valogne. The dimensions of the smaller valve, the only one found, measures 

 length 17, width 17 lines. 





