188 BRITISH PALAOZOIC FOSSILS. [Bracuioropa, 
size of exterior.—Fig. 1 a. Portion of superficial markings magnified.—Fig. 2. Ditto cast of interior shewing 
the two pairs of muscular impressions projecting.—Fig. 2 a. Portion of ditto shewing the impressions of the 
pallial vessels magnified. 
2nd Family. ORBICULID. 
Arms fleshy, spirally coiled one on each side, the parts united and fixed to one valve, leaving only the 
tips free, incapable of protrusion, provided with very long, close, sub-corneous ciliated fimbrize, without sup- 
porting apophyses ; shell conical, without hinge or deltidium, fixed by a muscle of attachment going out through 
an opening in the lower valve, which, though perforated, is proved to be the analogue of the imperforate 
valve of Terebratula, by having but two branchial vessels, and by the position of the alimentary canal. Hight 
adductor muscles, part of the anterior pair of which go out through the fissure and dilate into a disk 
for attachment; the large anterior and posterior pairs pass obliquely from one valve to the other without 
crossing ; within these are two slender pairs which decussate and slide the valves on each other. 
The muscles and viscera form a mass in the posterior half of the shell; the mouth is near the 
middle, and from each side of it the anterior crescentic pair of muscles diverge obliquely backwards ; 
behind the mouth is the trigonal green liver, and behind it the large grey ovary, and nearly at the 
posterior margin are the impressions of the small posterior pair of muscles; the stomach is large, pear- 
shaped, and from its posterior end a short curved intestine bends to the right side, and there opens 
between the lobes of the mantle; within the anterior crescent-shaped pair of muscles are two hearts, 
giving off two thick branching pallial veins to the perforated, and four to the imperforate valve, each 
with a small (?) artery attached to it. There is no trace in the shell, or fossils, of the existence of the arms. 
The family includes the following genera:—lIst, Siphonotreta; 2nd, Orbicella; 3rd, Orbiculoidea; 4th, 
Discina. 
Genus. SIPHONOTRETA ( Vern.) 
Gen. Char.—Shell elongate ovate, inequivalve, caleareo-corneous ; one valve slightly convex with no beak, 
the other with a produced beak, filled internally by a solid pad enclosing a tubular sheath for the pedicle, one 
end opening at the end of the beak of the great valve; substance obliquely punctured ; surface with scattered 
tubular spines. 
SrpHonotrReTA ANGLICA (Morris). 
Ref:.—Morris, Ann. Nat. Hist. 2nd Series, Vol. IV. t. 7. f. 1. 
Sp. Ch.—Longitudinally broad ovate: imperforate valve suborbicular, depressed; perforate valve ovate, very 
convex in the middle, most so about one-third from the beak; beak produced with a distinct perforation ; surface 
of both valves with minute close, imbricating, concentric striz, about fifteen in the space of one line, reticulated 
by minute close punctures, less than their diameter apart, their diameter equalling the width of the imbricating 
lines from each other. Length of perforated valve four lines, proportional width (greatest about the middle) 
=» length of small valve =, depth ,f. 
Mr Morris figures and describes long annulated setaceous spines, projecting from some of the lamin 
of growth, which the mode of preservation of our specimens renders invisible, although the marks of their large 
bases are seen scattered here and there; on the other hand, impressions taken from the cavities left by some 
of our specimens, shew the perforated tubular beak which he had not seen, and confirm his reference of the fossil 
to Stphonotreta. 
Position and Locality—Abundant in the shale nodules of Sunny Banks, Coniston. 
SIPHONOTRETA MICULA (M‘°Coy.) Pl. 1. H. fig. 3. 
Ref. id —M°*Coy, Ann. Nat. Hist. 2nd Series, Vol. VIII. p. 389. 
Sp. Ch.—Longitudinally ovate, length and width about equal; sides and front broadly rounded with 
a uniform curve, posterior extremity slightly acuminated; gently convex, perforated valve most so, greatest 
depth at about one-fourth the length from the beak, which is near the posterior margin, and perforated by a 
round tubular opening; surface marked with a few concentric waves of growth, and sharp flat regular con- 
