83. STREPTORHYNCHUS PAnpoRA (Billings). ~ 
Streptorhynchus Pandora (Billings), Canadian Journal, New Series, vol. v. p. 266, figs. 
12, 13. 
Streptorhynchus Chemungensis, var. Pandora (Hall), Pal. N.Y., vol. iv, Pl. IV, figs. 11, 
19; and Pl. IX, figs. 18, 25, and 27. 
: [Compare Strophomena Woolworthana (Hall), Pal. N. Y., vol. iii, Pl. XVI, figs. 
land 2]. ; 
Shell semi-oval, about one-fourth wider than long; the hinge-line equal to the greatest 
width of the shell, and forming right angles with the nearly straight sides, whilst the front 
margin is broadly rounded. Ventral valve elevated at the umbo, whence the surface slopes in 
all directions to the margin. Area of the ventral valve large and triangular, extending the 
whole length of the hinge-line. Foramen large, triangular, about twice as wide at the base 
as the height, nearly or quite closed by a convex deltidium. Dorsal valve moderately con- 
vex, slightly depressed towards the cardinal angles, with a narrow area. 
Surface marked by fine strongly elevated thread-like strie, which are sometimes alter- 
nately large and small, and which increase in approaching the margin both by bifurcation and 
interstitial addition. About four strize in the width of one line, sometimes more. 
“The interior of the ventral valve is marked by strong dental lamelle and a broad 
flabellate muscular impression, which in well preserved specimens shows the cordiform im- 
print of the adductors, and a short low mesial septum in the upper part. ‘The interior of 
the dorsal valve preserves deep dental sockets, with thick socket plates which support the 
duplicate cardinal process, each division of which is grooved at the extremity. There is like- 
wise a smgll process between the two branches of the cardinal process ; and below the hinge- 
line, the flabelliform muscular impression is divided by a low rounded mesial longitudinal 
ridge or obsolete septum.’”’ (Hall, Pal. NV. Y., vol. iv, p. 68.) 
Average specimens have a width of about an inch and a quarter by an inch in length, 
but largér individuals are known to occur. 
According to Hall, Streptorhynchus Pandora is merely a form of the vary variable S. 
Chenvungensis,(Conrad), There is, however, some doubt as to whether the specimens examined 
by Hall really belong to 8. Pandora, (Billings); since he states that the longitudinal striae 
are ‘‘crenulated by fine closely arranged concentric striz.” This is certainly not the case 
with any of the specimens which have come under my notice, and Mr. Billings explicitly 
notes the absence of concentric striae in the examples upon which he founded the species. 
Hall, also, states that a small central process exists between the two divisions of the cardinal 
process, but Mr. Billings states that no such process exists in S. Pandora. 1t thus remains 
uncertain whether the New York specimens are identical with these from Ontario. S. Pandora 
is nearly related to the well known European species S. crenistria, from which its only import- 
ant external difference is the absence of crenulating striz. 
Locality and Formation.—Corniferous Limestone, of Port Colborne, and Hagersville. 
Genus OntTHIS (Dalman). 
‘« Shell variable in shape, sub-cireular or quadrate ; valves equally or unequally convex ; 
socket valve sometimes slightly concave, with or without a mesial fold or sinus; hinge line 
straight, generally shorter than the width of the shell; both valves furnished with an area 
divided by a triangular open fissure for the passage of the pedicle fibres ; beaks more or less 
incurved, that of the larger valve generally more produced; surface, smooth, striated, or 
ornamented by simple, bifurcated, or intercalated ribs ; structure minutely or largely punc- 
tated; valves articulating by means of teeth and sockets. In the interior of the larger or 
ventral valve the vertical dental plates form the walls of the fissure, and extends from the 
beak to the bottom of the shell ; between these a small rounded mesial ridge divides the mus- 
cular scars, which extend over two elongated depressions margined on their outer side by the 
prolonged bases of the dental plates ; the cardinal muscles appear to have occupied the greater 
portion of the anterior division of these two depressions, the pedicle muscles occupying the 
external and posterior part of the same space; the adductor was probably attached to each 
side and close to the mesial ridge. In the socket valve the fissure is partially or entirely 
occupied by a more or less produced simple shelly process, to which were affixed the cardinal. 
