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 Productid^, J. E. Gray {partini), 1841. 



This group of Palliobranchs is typified by the genus Prodiictiis, as constructed by 

 Mr. James Sowerby. Mr. J. E. Gray, in the 'Catalogue of the British Museum,' 1841, 

 included in it the genus Calceola ; and of late the same author has made it to comprise 

 " the genera Produdus, Sow., Strophalosia, King, Chonetes, Fischer, Leptcena and OrtJds, 

 Dalman, Stropliomena, Rafinesque, and Calceola, Lamarck."^ Notwithstanding that 

 the high authority just quoted differs from me, I still feel it necessary to limit the 

 family to Produdus 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 Leptcsna analoga and Produdus horridus as examples illustrating the 

 characterism of the vascular system of their respective families, it may be predicated 

 of Strophomenida; that the primary pallial vessels are more or less confined to the 

 medio-longitudinal region of the valves ; and of Produdidce, 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 origin. Looking at the vein- 

 like line bounding the reniform lobes of Produdus horridus (PI. XI, fig. 10/) and 

 P. semirdiculatus (PI. XIX, fig. 3/), I cannot but think that these structures are each 

 due to a recurving vessel, rather than to an expanded and simply projecting vascular 

 organ, us appears to be the case in Criopus. 



Genus Produdus, J. Sowerby, 1814. 



Gbyphites, 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.) 



Produdus 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,' 



' Annals and Mag, of Nat. Hist., 2d series, vol. ii, p. 438. 



2 Annals and Mag. of Nat. Hist., vol. xviii, p. 28, 1846. 



3 Mineral Conchology, vol. i, p. 153, 1814. 



