LAMELLIBRANCHIATA. ] UPPER PALAZOZOIC MOLLUSCA. 515 
opposite ventral margin jj, width of posterior end ;;;, depth of both valves about the middle * (young shells 
more tumid and less elongate). 
The lengthened form and straight unsinuate ventral margin, and the side without any oblique concavity, 
distinguish this species with tolerable ease, as well as the greatest width being a little behind the beak, instead 
of from their apices. The specimen figured under the name Unio aquilinus of the Geological Transactions 
is broken at the posterior end, so as to appear a little shorter than it ought, but having the shell preserved 
it shews the remarkable tumidity of the dorsal margin, and the characteristic want of prominence of the beak, 
which is not so obvious in the internal casts originally figured by Sowerby. The short variety, or Sowerby’s 
figure 5 as above, is possibly a distinct species, and seems identical with the P. agrestes of Brown. The bifid 
anterior end, or cleft termination, alluded to by Capt. Brown in his P. antiquus is merely the impression of the 
anterior adductor, rendered visible by the removal of part of the shell. 
Position and Locality. Not uncommon in the carboniferous shale at Lowmoor near Bradford. 
CARBONICOLA SUBCONSTRICTA (Sow. Sp.) 
Ref. and Syn. = Unio subconstrictus Sow. Min. Con. t. 33. f. 2, 3.= Pachyodon Amygdala Brown, An. Nat. 
Hist. Vol. XII. t. 16. f. 3. =P. subtriangularis id. ib. t. 16. f. 6. =var. 8. P. Hmbletoni id. ib. t. 16. f. 9; 
var. a. = P. agrestis id. ib. t. 16. f. 11; var. robusta = Unio id. Sow. Geol. Trans. Vol. V. t. 39. f. 14. 
Dese.—Ovato-subtrigonal ; anterior side short, rounded ; beaks large (most prominent and widely separated 
in the casts); posterior end obliquely subtruncate, narrowed by the convergence of the dorsal and ventral 
margins; ventral margin convex in the anterior half, concave in the posterior half, forming a gentle sinus in 
front of the respiratory angle, from which sinus a shallow depression extends obliquely forwards to within half 
or three-quarters of an inch of the beak, most strongly marked towards the margin of old individuals; valves 
moderately convex, most so a little below the beaks, becoming gradually compressed towards the margin ; 
posterior slope very convex near the dorsal margin in casts, but obtusely angulated along the same line when the 
shell is present ; substance of the shell very thick ; surface concentrically marked with coarse, irregular, unequal 
strize, and small plicze of growth, most prominent towards the margin of large specimens. Casts shew the thick 
cardinal tooth, and slender, elongate, lamellar, lateral teeth ; simple pallial scar ; and two adductors, each sur- 
mounted by a small accessory impression, as in the generic character. Length of small specimen (corresponding 
with Sowerby’s original type) one inch four lines, proportional width from beak to opposite point of ventral margin 
#2, width of posterior end ;3, length of anterior end about ,{;, depth of both valves ;;;. 
This species varies slightly in the strength of the sinus and proportional width. When the shell is pre- 
served there is always the obtuse angle along the dorsal margin, alluded to by Goldfuss and de Koninck as a 
characteristic of their Unio tellinaria, which I suspect will be found referrible to this one species. 
The somewhat larger specimens, the references for which I have marked above as var. 8, seem a little 
longer in proportion (length one inch nine lines, proportional width of casts without the shell ;{;, depth of both 
valves %); but I have no doubt they are an advanced age of the same species, and are intermediate between 
Sowerby’s original type and his species U. robustus. 
Position and Locality — Very common in the coal-shale of Bradford, Yorkshire, 
Var. Rosusta (Sow. Sp.) 
Ref. and Syn, = Unio robustus Sow. Geol. Trans. t. 39. f. 14. 
This variety is in fact, in my opinion, only the adult age of the species originally figured as Unio subcon- 
strictus by Sowerby, or when it attains a width from beak to margin of one and half inch. The figure of 
U. robustus in the Geological Transactions seems much shorter and deeper than natural from the posterior 
end being broken off obliquely; the true outline may be seen by following the lines of growth in the same 
figure at one and half inch or nine lines from the beak. 
