240 BRITISH PALAOZOIC FOSSILS. [Bracnrorops. 
marked with very large punctures, which form close punctured lines from the beak to the margin in casts ; about 
thirty strie in the space of two lines at three lines from the margin: receiving valve with a very short mesial 
septum, about one-fifth the length of the shell, and two dental lamelle diverging at about 100°, forming the 
anterior lateral boundaries of two very short, diverging, ovate, muscular impressions, reaching rather more than 
one-third the length of the shell. Width seven lines, proportional length 5, depth of receiving valve =; to *,, 
depth of entering valve ;3,. 
Mr Sowerby states that both valves of his shell are convex, which, if correct, would render his species 
distinct from that before us, which has the distinctly marked hinge of Leptena, with both valves curved in the 
same direction. In form it strikingly resembles the Leptena (Chonetes) lata of the Ludlow rocks, but is 
destitute of spines on the hinge-line, and is easily distinguished by the much greater fineness of the strize, or the 
greater number in a given space. When the larger strize can be distinctly seen, which is not often the case, the 
resemblance is very strong to Leptena sericea, from which it differs in the flatter entering valve, in the fine, more 
equal strize, without the larger strize, and in the distinct, radiating, coarsely-punctured lines of the interior, and 
the small size of the bilobed muscular impressions of the receiving valve, which however it resembles in form. 
If, as I suspect, the Orthis lata be a Leptena, it cannot bear that specific name already in use for one of the 
best-known species; and as I have little doubt that the O. tenuissimestriata, which I originally figured from 
unusually large and much-compressed specimens, in which the striation was still more delicate, is referrible to 
an extreme variety of the same species, that name may be conveniently retained for the species. I cannot 
imagine why Mr Salter (Mem. Geol. Surv. Vol. II. p. 289) unites this species to O. protensa, which has vastly 
coarser, fasciculated, strize, &c. 
Position and Locality—Caradoc sandstone of top of Moel Seisiog, Llanrwst, Denbighshire ; Bala lime- 
stone of Llandeilo, Caermarthenshire ; common in the Caradoe limestone of the Hollies, Church Stretton, 
Shropshire; Bala sandstone of Pont y Meibion, S. of Llansantfraid, N. Wales; olive Bala schists of Cefn 
Grugos, W. of Llanfyllin, Montgomeryshire; Bala flags of Llandeilo; Bala schists of Y Foel Fawr, near 
Llanrhaider ; Bala limestone of Coniston, Lancashire. 
Explanation of Figures —P1. 1. H. fig. 44. Natural size from Llandeilo ; fig. 44 @, internal cast of ditto ; 
fig. 440, surface of ditto, magnified, shewing the punctured sulci left by the removal of the shell in the upper 
portion; fig. 44 c, longitudinal section. 
LEPTANA TRANSVERSALIS (Dal.) 
Ref. and Syn.—Dalman, Act. Holm. t. 1. f. 4. Sil. Syst. t. 13. f. 2; 
+ L. duplicata Sow. Sil. Syst. t, 22. f. 2. (2L. lepisma Sil. Syst. Young). 
Sp. Ch.—Transversely fusiform, globose; hinge-line as wide as the shell; cardinal angles acute, nearly 
smooth near the beaks; both valves radiated with several slender thread-like ridges, about half a line apart 
at the margin, and a line, or two-thirds of a line, apart at three lines from the beak, at which distance, 
in finely-preserved specimens, about twenty-three very minutely-punctured longitudinal strie may be detected 
in the space of one line, which are usually invisible, even with a moderately strong lens ; cardinal area low, 
triangular in each valve; the two areas subparallel with each other at their point of union, curved nearly 
into the plane of the lateral margins, that of the receiving valve scarcely one-third greater than that of 
the entering valve; triangular foramen in the receiving area closed towards the apex by a small pseudo- 
deltidium, and below by the large rostral tooth of the entering valve : cast of receiving valve with two short 
cardinal teeth, diverging at 90°, from the ends of which a W-shaped groove (impression of a ridge on the shell) 
forms the lateral and anterior boundary of the remarkably small, obscurely bilobed, pentagonal, muscular 
impressions, which are slightly wider than long, and their length less than one-third that of the shell, the 
sinus in the front margin short, diverging at about 105° from the muscular impression ; hinge-line crenulated 
near the beak; inner surface coarsely radiated, between which are irregularly placed numerous pits, or extremely 
large punctures, the extreme margin being marked with fine longitudinal lines, and close, numerous, minute 
punctures : interior of entering valve with two very prominent, oval ridges, bounding the muscular impressions, 
