86 PERMIAN FOSSILS. 
Discina speluncaria occurs at Thrislington Gap, in the Marl Slate; at Garmundsway 
(the locality of the above-noticed specimens), in the overlying beds of compact Lime- 
stone ; and at Tunstall Hill, in the Shell-limestone. It was first noticed by Schlotheim 
at Gliicksbrunn: it has also been found at Ilmenau and Corbusen, in the lower Zechstein 
(Geinitz). 
Family Propuctipa#, J. BE. Gray (partim), 1841. 
This group of Palliobranchs is typified by the genus Productus, as constructed by 
Mr. James Sowerby. Mr. J. HE. Gray, in the ‘ Catalogue of the British Museum, 1841, 
imcluded in it the genus Ca/ceo/a ; and of late the same author has made it to comprise 
“the genera Productus, Sow., Strophalosia, King, Chonetes, Fischer, Leptena and Orthis, 
Dalman, Strophomena, Rafinesque, and Calceola, Lamarck.’ Notwithstanding that 
the high authority just quoted differs from me, I still feel it necessary to limit the 
family to Productus and Strophalosia, as proposed in my former paper,’ considering that 
these genera differ from all the others above named in their reniform impressions, 
which obviously constitute a capital family diagnosis. 
Taking Leptena analoga and Productus horridus as examples illustrating the 
characterism of the vascular system of their respective families, it may be predicated 
of Strophomenide, that the primary pallial vessels are more or less confined to the 
medio-longitudinal region of the valves; and of Productide, that they strike off at the 
moment they issue from between the muscular scars, in a lateral direction, running for 
some distance nearly parallel to the cardinal line, then curving forward, and round 
toward the centre, and finally returning to nearly their origm. Looking at the vein- 
like line bounding the reniform lobes of Productus horridus (P\. XI, fig. 10/7) and 
P. semireticulatus (Pl. XIX, fig. 3.7), I cannot but think that these structures are each 
due to a recurving vessel, rather than to an expanded and simply projecting vascular 
organ, as appears to be the case in Criopus. 
Genus Productus, J. Sowerby, 1814. 
Grypuites, Walch. 
Anomites, Martin. 
Diagnosis.—*“ An equilateral unequal-valved bivalve, with a reflexed, more or less 
cylindrical margin. Hinge transverse, linear. Beak imperforate; one valve convex, 
the other flat or concave internally.”’ (J. Sowerby.) 
Productus longispinus is the first species described and figured by Mr. J. Sowerby 
under the head of this genus; but from what is stated in the ‘Mineral Conchology,’ 
1 Annals and Mag. of Nat. Hist., 2d series, vol. u, p. 438. 
2 Annals and Mag. of Nat. Hist., vol. xviii, p. 28, 1846. 
3 Mineral Conchology, vol. i, p. 153, 1814. 
