Bracutovopa. | UPPER PALZOZOIC MOLLUSCA. 453 
appearing only alternately larger and smaller (about twelve to fourteen in two lines), separated by concave 
spaces, about equalling them in width. Casts shew the dental lamelle in the entering valve diverging at an 
angle of 75°, and reaching about one-fourth of the length of the shell; the mesial septum between them just the 
same length; the dental lamellee of the beak of receiving valve diverge at only 26°, and reach rather less than 
one-third the length of the shell; the mesial septum between them is only three-fourths of their length. Width 
two inches three lines, proportional length of receiving valve ; to %, length of entering valve = to %, height 
of cardinal area ;, to ;;, depth of receiving valve = to %, depth of entering valve 72. 
This species is so totally different from the 8. crenistria, by its greatly elevated area, strongly convex 
entering valve, and irregularly convex receiving one, oblique distortion of the beak, and extremely irregular 
distorted mode of growth, evinced by the two or three great concentric irregular undations, that it is difficult 
to conceive how they could be confounded. The shell is extremely thin, so that traces of the striz and all the 
irregularities of the surface are reproduced on the cast. This is one of the irregular growing species, for which 
Professor King forms his genus Streptorhynchus. I am unable to say whether there is, or is not, a small 
foramen in the apex of the beak. ‘The striation has a general resemblance to that of the S. erenistria, but the 
rough matrix of the specimen renders me uncertain whether there is any sharp concentrie striation. 
Position and Locality—Not uncommon in the lower carboniferous limestone of Kendal. 
Subgenus. LEPTAGONIA. See page 247. 
LepT&NnA (Lepiagonia) ANALOGA (Phill.) See Devonian Section, p. 389. 
Position and Locality—Common in the lower carboniferous limestone of Derbyshire ; common in the dark 
carboniferous limestone of Ronalds-way, Isle of Man. 
Var.a. DISTORTA (Sov.) 
Reef —Sow. Min. Con. t. 615. f. 3. 
Position and Locality—Common in the middle carboniferous limestone of Poolwash, Isle of Man. 
Var. B. MULTIRUGATA (J/°Coy). 
Ref.—M°Coy, Synop. Carb. Foss. Irel. t. 18. f. 12. 
It is quite possible that this shell, which I at one time thought a distinct species, may form an extreme 
variety of the present species. It is characterised by the regular flatness of the visceral disk, and the great 
number and regularity of the concentric wrinkles, which are from twenty-two to twenty-four on a visceral disk 
eight lines long ; the ridges usually unite in pairs as they approach the hinge-line. The longitudinal strize are 
nine or ten in two lines at the front margin of disk. 
Position and Locality—Rare in the carboniferous limestone of Kendal. 
Lerrana (Leptagonia) stxuata (de Kon.) 
Ref —Leptena id. de Kon. Anim. Foss. Bel. Sup. t. 56. f. 2. 
Dese.—Subquadrate ; visceral disk rhomboidal, flattened, entirely covered with numerous, strong, irregular, 
occasionally interrupted, concentric wrinkles (about fourteen or fifteen) ; a wide, deep, mesial hollow extends 
nearly from the beak, the sides are slightly convex, but again separated from the abruptly-flattened ears by 
a marked depression, the line of junction between the ears and the body of the shell occasionally marked 
by a few large spine tubercles; beak scarcely projecting beyond the hinge-line, which slightly exceeds the 
width of the shell in flattened rounded ears; front short, abruptly deflected nearly at right angles from the 
visceral disk, and deeply indented by the wide mesial furrow. Whole surface marked with coarse, obtuse, sub- 
equal, longitudinal strize, eight in two lines at angle of front. Entering valve resembling the receiving one in 
shape and markings, leaving a very small space for the animal; cardinal area ten times wider than high; 
