390 BRITISH PALAOZOIC FOSSILS. [ Bracutopops. 
This family must either be limited to the genus Productus, or include (in accordance with Mr J: E. Gray’s 
view) all the Orthisidw ; the characters of Professor King’s genus Strophalosia seem so perfectly to unite the 
characters of the two families, that it is quite possible the latter course may become inevitable. M. d’Orbigny 
proposes as a character for separating the Orthisidw from the Productide, that the former have the shell fibrous 
and the latter punctured, but they are both punctured distinctly. 
Genus. PRODUCTA (Sow.) 
Gen. Char.—Very inequivalve ; receiving valve subhemispherical, and covered with scattered nacreous 
hollow tubular spines; entering valve concave ; hinge-line straight, usually as long as the shell is wide; no 
cardinal area nor foramen; ¢nternally, entering valve with a projecting bilobed lever-like beak, from which a 
long, low, mesial septum extends nearly to the front; about the middle of this is on each side a small 
pear-shaped apophysis or protuberance, probably giving rise to the arms; a little outside and anterior to those 
are two pear-shaped or sickle-shaped smooth impressions, usually with a raised outer margin, curving outwards 
and forwards, and probably marking the place of a pair of arm-like lobes, as in the recent Thecidea ; exterior 
to these, the surface is punctured and spinulose; between the little apophyses at probable base of arms, and 
the beak, close to the septum on each side, is a complex dendritically-lobed impression, supposed by some to 
mark the ovaries, by others, the liver, and by others, muscular attachments. The receiving valve has near 
the beak two dendritic impressions like those of the opposite one, and on the most convex part of the valve on 
each side a pair of very large muscular impressions so close together as only to form one protuberance on 
each side, but readily distinguishable ; the anterior pair, or portion, largest, rounded, and more closely sulcated ; 
the posterior pair or portion nearest the beak, smaller, depressed, triangular, and probably sending their fibres 
to the prominent beak of the entering valve to open it. 
I am uncertain of the points of insertion of the adductor muscles in the entering valve, but think it likely 
they were fixed to the little polished protuberance close to the middle of the septum on each side, from their 
close resemblance in density and structure to the boss on the beak of the valve, which we know received 
the tendons of the adductors. Each valve is composed of several parallel layers, separable in some states 
of preservation ; punctures of the shell scattered, large; intervening strata dense. 
PRopUCTA PRALONGA (Sow. Sp.) 
Ref. and Syn.=Leptena prelonga Sow. Geol. Trans. 2nd Series, Vol. V. t. 53. f. 29? = Productus Christiani 
(de Kon.) Mong. du Prod. t. 17. f. 3. 
Sp. Ch.—Subeylindrical, or oblong; hinge-line equal to the width of the shell, forming short, much de- 
pressed, rectangular ears ; receiving valve with a very large inflated beak, gradually arching into the produced, 
rounded, semicylindrical front; a narrow, rounded, mesial ridge extends nearly from the beak to the margin ; 
entering valve with the mesial disk flattened or slightly concave, the produced front bending rather abruptly 
downwards, the deep, narrow, concave, mesial sinus (corresponding to the ridge of opposite valve) very distinct 
nearly from the beak ; visceral portion of both valves faintly and irregularly wrinkled concentrically ; surface 
marked with fine, close, slightly irregular, longitudinal strize (ten or twelve in two lines at one inch from the 
beak), and several small, ovate, scattered spine bases, principally on the rostral portion, where they are larger 
and closer, three or four of the largest on the mesial fold. Width (of small specimen) one inch one line, 
length of visceral portion of entering valve nine lines, length of deflected front seven lines, distance between 
the valves in rostral portion six lines. 
I was greatly surprised to find, on examining the unique specimens of this species in the Cambridge 
collection, originally figured and described by Sowerby, that the impression of the entering valve (not figured) 
shews a strong, narrow, rounded mesial ridge of exactly the size and shape of that in the P. mesoloba (a very 
slight indication of which may be now recognised in a notch in the lower margin of Sowerby’s end view), and 
further, that along the corresponding line on the middle of the receiving valve there was a narrow, rough, 
abraded space, from which there could be no doubt the narrow ridge had been either broken in extracting the 
