PRODUCTID^. 333 



tered; hiuge-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 bj^ 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. P. sfriatus is 

 irregular in its growth, elongated and tapering towards the beak, 

 and occurs in numbers packed closely together. P. prohoscideus 

 seems to have lived habitually in cavities, or half-buried in mud, 

 as suggested hy M. d'Orbign}^ ; 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, 1867. Like Productus, but hinge-margin 

 with teeth ; both valves with area, the larger one with deltidial 

 opening ; kidney-shaped impressions very broad. P. subacideata. 

 March. Devon. 



Strophalosia, King, 1844. 

 Syn. — Orthothrix, Geinitz, 1848. Leptsenalosia, King, 1845' 

 Distr. — Fossil, 8 sp. Devonian — Carb. ; Europe, Himalaya 

 (Gerard). S. excavata, Geinitz (cxxxix, 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, Hclmerscn, 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. Wangenheimii, Vern. (cxxxix, 

 67, 68). Permian; Russia. 



Chonetes, Fischer, 1837. 



Etym. — Ghone, a cup. 



Dish'. — Fossil, 47 sp. Silurian — Carboniferous; Europe, North 

 America, Falkland Islands. G. striatella, Dalm. (cxxxix, 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 covered ; 

 interior punctate-striate ; vascular impressions very small. — 

 Davidson. 



