248 BRITISH PALALOZOIC FOSSILS. { Bracutopopa. 
Lept@na (Leptagonia) DEPRESSA (Dal. Sp.) 
Ref. and Syn. = Productus depressus Min. Con. t. 459. = Leptena depressa Sil. Syst. t. 12 f. 2. 
+ L. tenuistriata Sow. Sil. Syst. t. 22. f. 2a. + L. rugosa (Dal.). 
Sp. Ch.—Square, prismatic; rostral portion quadrate ; sides and front margin nearly straight, slightly 
undulated ; slightly convex near the beaks; irregularly concaye before reaching the angle, which is seldom 
as high as the surface near the beak; concentric wrinkles, about twelve to fifteen, strong, rounded, slightly 
undulated, and some of them occasionally interrupted in parts, following the direction of the margin, and 
turning abruptly outwards near the cardinal line; deflected front prismatic ; sides subparallel, or slightly 
converging towards the front margin, which is flattened, or with few irregular longitudinal folds, dilated at the 
cardinal angles into flattened ears; longitudinal striz coarse, obtuse, equal, about nine to twenty (usually 12) 
in the space of two lines at the edge of the rostral portion: interior of receiving valve with two short cardinal 
teeth, diverging at 115°, from the ends of which a slender prominent ridge curves forwards and inwards on each 
side, forming the boundary of the rather large, ovate, adductor impressions, which reach about half the length of 
the rostral portion, the two being separated by a mesial ridge extending rather less than their length ; interior 
of entering valve with the rostral portion very concave, and sharply defined from the deflected front, by a 
prominent narrow margin; rostral tooth very large, and deeply bifid; the pits for the teeth of the opposite 
valve are flanked anteriorly by two thick ridges, which gradually incurve, forming the tubercular boundary to 
the rounded posterior pair of muscular impressions; anterior to which are the much smaller anterior pair 
of ovate impressions, with tumid boundaries; the mesial separating ridge extending two-thirds the length 
towards the deflected edge, which latter bears numerous fine, nearly straight, linear, simple or once-branched, 
pallial impressions, about twice the size of the external strize ; inner surface of both valves with small spinulose 
tubercles ; cardinal area moderately large in both valves. Average width of flat rostral portion at cardinal 
angles one inch three lines, proportional width of ditto at middle 7, length of ditto ;,, length of deflected 
front =. 
In some states of preservation, or partial decomposition, each of the longitudinal strize seems divided into 
two, giving rise, I have no doubt, to the species L. tenwistriata (Sow.), but by far the greater number of 
specimens in the Caradoc and Bala rocks only shew, on accurate measurement, the same number of strice 
in a given space as the Wenlock specimens. Some specimens in which the front is gradually rounded into 
the sides agreeing with LZ. rugosa (Dal.), differ in no other respect from the normal specimens, and the passage 
is so gradual and obviously unimportant, that I have no doubt of the specific identity of the forms. Some 
specimens have the muscular impressions narrower, and the dental lamellie diverging at a less angle than above, 
and varying in length from little more than one-third to nearly two-thirds the length of the visceral disk. The 
variety with wide muscular impressions, has them varying also from less than one-half to more than one- 
half the length of the visceral disk. These varieties do not at all accord with any of the changes of form 
or striation noted; nor is there any relation between the fineness of the striation and the geological position, 
although, generally speaking, the fine striation is most common in specimens from the old beds. 
Position and Locality—Common in the Wenlock limestone of Woolhope; very common in the Wenlock 
limestone of Dudley, Staffordshire; in the green Ludlow rock of Parklane, Llandeilo, Caermarthenshire ; 
in the greenish Bala slates of Cefn Coedog, Corwen, N. Wales; Bala flags, three miles N. of Builth, 
Radnorshire; Bala schists of Rhosfawr, N. of Glog, Llanfyllin, N. Wales; Ludlow rock of Keeper's Lodge, 
Goldengrove, Llandeilo, Caermarthenshire ; common in the Bala slates of Cyrn y Brain, Wrexham, Denbigh- 
shire; Bala schists of Gelli Grin, Bala, Merionethshire; schists of Wilfa, Penmachno, N. Wales; Bala slates 
of Blain y Cwm, W. of Nantyre, Glyn Ceiriog, S. of Llangollen, Denbighshire; in the Wenlock limestone 
of Wenlock, Shropshire ; Bala schists of Penlan, Llandovery, S. Wales; Bala limestone of Coniston Water- 
Head, Lancashire; Bala slates of Llansantfraid, Glyn Ceiriog, S. of Llangollen, Denbighshire ; Bala schists of 
Bryn Melyn, near Bala, Merionethshire; Bala schists of Corwen, Merionethshire; Caradoc sandstone of 
Horderly ; common in the Bala limestone of Mathyrafal-ffridd, S. of Meifod, Montgomeryshire ; Bala schists, 
