PRODUCTID A. 833 
tered ; hinge-area in each valve linear, indistinct; no hinge-teeth ; 
cardinal process lobed, striated; vascular impressions simple, 
curved ; ventral valve deep, with two rounded or subspiral cavi- 
ties in front. These shells may have been attached by a pedicel 
when young, the impressions of the pedicel-muscle blending 
with those of the hinge-muscles in the ventral valve. A few 
species appear to have been permanently fixed. VP. striatus is 
irregular in its growth, elongated and tapering towards the beak, 
and occurs in numbers packed closely together. P. proboscideus 
seems to have lived habitually in cavities, or half-buried in mud, 
as suggested by M. d’Orbigny; its ventral valve is prolonged 
several inches beyond the other, and has its edges rolled together 
and united, forming a large permanently open tube for the 
brachial currents. The large spines are most usually situated 
on the ears of the ventral valve, and may have served to moor 
the shell; being tubular they were permanently susceptible of 
growth and repair. Although edentulous, the dorsal valve must 
have turned on its long hinge- line with as much precision as in 
those genera which are regularly articulated by teeth. 
PRODUCTELLA, Hall, 186 7. Like Productus, but hinge-margin 
with teeth ; both valves with area, the larger one with deltidial 
opening ; kidney -shaped i impressions very broad. P. subaculeata. 
Murch. Devon. 
SrrRopHALosr4, King, 1844. 
Syn.— Orthothrix, Geinitz, 1848. Leptenalosia, King, 1845- 
Distr.—Fossil, 8 sp. Devonian—Carb.; Europe, Himalaya 
(Gerard). S. excavata, Geinitz (exxxix, 66). 
Shell attached by the umbo of the ventral valve ; subquadrate ; 
covered with long slender spines; valves articulated, dorsal 
moderately concave, ventral convex, each with a small area; 
fissure covered ; vascular impressions conjoined, reniform. 
AULOSTEGES, Helmersen, 1847. Shell like Productus; ventral 
valve with a large, flat, triangular hinge-area with a narrow convex 
pseudo-deltidium in the centre; beak a little distorted, as if 
attached when young; dorsal valve slightly convex near the 
umbo ; interior as in Productus. S. Wangenheimit, Vern. (exxxix, 
67,68). Permian; Russia. 
CHoNneETES, Fischer, 1837. 
Etym.—Chone, a cup. 
Distr.—Fossil, 47 sp. Silurian—Carboniferous; Europe, North 
America, Falkland Islands. (C.striatella, Dalm. (OXxxix, 69-71). 
Shell transversely oblong, with a wide and straight hinge- line ; 
area double; valves radiately striated, articulated ; hinge- margin 
of ventral valve with a series of tubular spines ; fissure cov ered ; 
interior punctate-striate; vascular impressions very small.— 
DAVIDSON. 
