332 PRODUCTID^. 



Ampliiclina resembles some Lept^nse,the shell-structure is very 

 similar. 



PoRAMBONiTES, Pander, 1830. 



Syn. — Isorhynchus, King, 1849. 



Distr. — 8 sp. Lower Silurian; Russia and Portugal. P. 

 sequirostris^ Schloth. (cxxxix, 58). 



Shell impunetate ; surface minutely pitted ; each valve with a 

 minute hinge-area and indications of two septa; foramen angular, 

 usually concealed, 



Syntrielasma, Meek and Worthen, 1865. 



Dintr. — Carbonifei'ous ; N. and S. America. B. heviiplicatus, 

 Hall (cxxxix, 59, 60). 



Shell thin, gibbous or subglobose, in adult specimens ; valves 

 articulated by teeth and sockets ; hinge-line straight and very 

 short ; area small, partW 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 laminae 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. 



Family PRODUCTID^. 



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. 



Productus, Sowerby, 1814. 



/Si/??. — Protonia, Link, 1830. Arbusculites, Murray, 1831. 



Distr. — Fossil, 81 sp. Devonian — Permian; N. and S.Am., 

 Europe, Spitzbergen, Thibet, Australia. P. giganteus, Sowb. 

 (cxxxix, 61, 62). P. horridus, Sowb. (cxxxix, 63-65). 



Shell free, auriculate, beak large and rounded ; spines scat- 



