198 HISTORICAL PALHONTOLOGY. 
Amongst the A/o//usca, the remains of Pofyzoa may fairly be 
said to be amongst the most abundant of all the fossils of the 
Permian formation. The principal forms of these are the 
fronds of the Lace-corals (Fenestella, Retepora, and Synocladia), 
which are very abundant in the Magnesian Limestone of the 
north of England, and belong to various highly characteristic 
species (such as Fenestella retiformis, Retepora Ehrenbergt, and 
Synocladia virgulacea). The Brachiopoda are also represented 
in moderate numbers in the Permian. Along with species of 
the persistent genera Déscina, Crania, and Lingula, we still 
meet with representatives of the old groups Sfzr7fera, Athyris, 
and Streptorhynchus ; and the Carboniferous /roducte yet 
survive under well-marked and characteristic types, though in 
much-diminished numbers. The species of Brachiopods here 
figured (fig. 135) are characteristic of the Magnesian Limestone 
in Britain and of the corresponding strata on the Continent. 
lig. 135.—Brachiopods of the Permian formation. a, Producta horrida; b, Lingula 
Crednert ; c, Terebratula elongata; d and e, Camarophoria globulina. (After King.) 
Upon the whole, the most characteristic Permian Brachiopods 
belong to the genera Producta, Strophalosia, and Camaro- 
phoria. 
The Bivalves (Lamellibranchiata) have a tolerably varied 
development in the Permian rocks; but nearly all the old 
types, except some of those which occur in the Carboniferous, 
have now disappeared. The principal Permian Bivalves 
belong to the groups of the Pearl Oysters (Aviculide) and the 
Trigoniade, represented by genera such as Bakewellia and 
Schizodus; the true Mussels (JZyiilide), represented by species 
which have been referred to AZpii/us itself; and the Arks 
(Arcade), represented by species of the genera 47ca (fig. 136) 
and Ayssoarca. The first and last of these three families have 
a very ancient origin; but the family of the Z7zgonzade, though 
