386 BRITISH PALAZOZOIC FOSSILS. [Bracuiopopa. 
This beautifully distinct species is easily distinguished from the O. crenistria by the near equality of all 
its strie, which are finer, closer, and want the number of fine intermediate longitudinal strie. From the 0. 
subarachnoidea it differs in its wider, more quadrate form, and broad slightly convex front. 
Position and Locality—Not uncommon in the slate of Lanlake, Launceston, and in the same beds at 
South Petherwin. 
LeptaNna (Strophomena) aicas (M°Coy). Pl. 2. A. fig. 7. 
Sp. Oh.—Rotundato-trigonal ; hinge-line equal to the width of the shell; sides gently convex, converging 
to a narrow, much rounded front; valves much flattened, slightly convex ; surface radiated with very numerous, 
fine, close, obtuse striee, separated by narrower, finely punctured, impressed lines, every fifth, seventh, or ninth of 
which seems larger than the rest ; about sixteen strize in two lines at an inch from the beak, fifteen in the same 
space at the margin, three inches from the beak ; cardinal area broad ; internal casts of receiving valve in adult 
specimens shew the pair of muscular impressions, forming a slightly bilobed, or subtrigonal mass, about one- 
third wider than long, and reaching rather more than one-third the length of the shell, each side marked with 
six or seven very coarse radiating ridges ; mesial septum very small. Average length three inches two lines, 
proportional width 2 to #8, width of cardinal area nearly two lines, 
This gigantic species in its elongate, elliptical, or subtrigonal form, arising from the narrow rounded front, 
precisely agrees with Orthis subarachnoidea of MM. dArchiac and de Verneuil (Geol. Trans. 2nd Series, Vol. VI. 
t. 36. f. 3), but differs from it in the larger strize at subregular intervals between the groups of smaller, as well as 
in its great size. I have seen and made drawings of a large number of specimens in the private collections of 
persons at or near Looe, although there is only one poor specimen in the university collection; I am therefore 
better prepared to decide on the characters of the species than I should otherwise have been. 
Position and Locality—Common in the Devonian shale of Looe ; Devonian shale of Polruan, Cornwall. 
Explanation of Figures.—PI. 2. A. fig. 7, natural size of average specimen; the lower portion netted by 
a species of Vioa. 
LEePTHNA (Strophomena) Nopiuis (M*Coy). Pl. 2. A. fig. 8. 
Sp. Ch.—Semicylindrical ; entering (2) valve very gibbous near the beaks, strongly-arched downwards into 
a subeylindrical, deflected front, the sides of which are slightly flattened to join the obscurely-defined ears, which 
project from the gibbous beak, and are nearly rectangular; front rounded; surface radiated with narrow, dis- 
tinctly defined ridges, of about equal thickness throughout, about twenty originating from the beak, between 
each pair of which, after about the length of one inch, a new ridge equal to the primary in size is developed, so 
that nearly over the whole shell the subequal ridges are little more or less than a line apart, the intervening 
spaces slightly concave, three times wider than the ridges, crossed by very deep, strong, irregularly curved, 
concentric wrinkles, not crossing the ridges, scarcely four in a longitudinal space of three lines; entire surface, 
ridges and furrows, marked with very fine, slightly irregular, longitudinal, distant strize, nine in the space of one 
line, strongly punctured when the outer layer of shell is remoyed. Width at hinge-line two inches four lines, 
proportional length about the same, depth (greatest at one-third from the beak) jj. 
This fine species is so completely unlike any other, that it is unnecessary to point out the distinctions, 
the nearest analogue apparently being the comparatively little, flat, few-ribbed Orthis undulata (M°Coy) Synop. 
Sil. Fos. Irel. t. 3. f. 22. of the Silurian series, with which however it has no specific affinity. 
Position and Locality.—Rare in the Devonian limestone of Teignmouth. 
Explanation of Figures.—P|. 2. A. f. 8, natural size; fig. 8, portion of surface of ditto magnified, 
shewing the longitudinal striation of the surface, and the lines of punctures where the shell is decorticated. 
Leeramna (Strophomena’) SORDIDA (Sow) 
Ref. and Syn. =Leptana sordida Sow. Geol. Trans. 2nd Series, Vol. V. t. 53. f. 5, 16. 
Sp. Ch.—Transversely oblong or semielliptical ; depressed, or slightly convex, entering valve most so ; 
front wide, slightly convex; lateral margins slightly convex, sometimes front and lateral margins uniformly 
