332 PRODUCTID A. 
= 
Amphiclina resembles some Leptzenee, the shell-structure is very 
similar. 
PoORAMBONITES, Pander, 1830. 
Syn.—Isorhynchus, King, 1849. 
Distr.—8 sp. Lower Silurian; Russia and Portugal. P. 
equirostris, Schloth. (¢xxxix, 58). 
Shell impunctate ; surface minutely pitted; each valve with a 
minute hinge-area and indications of two septa; foramen angular, 
usually concealed. 
SyntTrRiELASMA, Meek and Worthen, 1865. 
Distr.—Carboniferous ; N. and 8. America. S. hemiplicatus, 
all (exxxix, 59,60). 
Shell thin, gibbous or subglobose, in adult specimens; valves 
articulated by teeth and sockets; hinge-line straight and very 
short; area small, partly common to both valves, but higher in 
the ventral valve, where it is divided by a triangular, open 
foramen; beaks incurved, subequal; surface radiately plicate, 
‘and striate, the middle plication of the dorsal valve larger, with 
corresponding sinus of the other valve; socket- plates of the 
dorsal valve much as in Orthis, being quite prominent and very 
diverging, with a linear, longitudinal, ‘mesial ridge between them ; 
dental laminee of the ventral valve thin, prominent, very closely 
approximate at their connection with the bottom of the valve, 
and with a similar mesial septum, extending as three nearly 
parallel plates to the middle of the valve ; muscular and visceral 
impressions unknown ; shell-structure distinctly punctate. 
Famity PRODUCTID A. 
Shell concavo-convex, with a straight hinge-line ; valves rarely 
‘articulated by teeth ; closely appressed, furnished with tubular 
spines; ventral valve convex; dorsal concave ; internal surface 
‘dotted with conspicuous, funnel-shaped punctures ; dorsal valve 
with a prominent cardinal process; brachial processes (?) sub- 
‘central; vascular markings lateral, broad, and simple; adductor 
impressions dendritic, separated by a narrow central ridge ; 
ventral valve with a slightly notched hinge-line; adductor scar 
central, near the umbo; cardinal impressions lateral, striated. 
Propuctvus, Sowerby, 1814. 
Syn.—Protonia, Link, 1830. Arbusculites, Murray, 1831. 
Distr.—Fossil, 81 sp. Devonian—Permian; N. and 8. Am., 
Europe, Spitzbergen, Thibet, Australia. _P. giganteus, Sowb. 
((Cxxxix, 61,62). P. horridus, Sowb. (exxxix, 63-65). 
Shell free, auriculate, beak large and rounded; spines scat- 
