DESCRIPTIVE REMARKS. lxxvil 
species which appears to be confined to Permian strata. ‘The fossil 
named Lénestella retiformis has been found by Mr. J. W. Kirkby* to be 
identical with a characteristic Carboniferous species Fenestella plebeia 
M‘Coy, a species the author believes to be a synonym of Fenestella 
antiqua, figured on Pl. xxxvii., fig. 1. 
With respect to the Brachiopoda, Mr. Davidson enumerates but 
seventeen species as occurring in British Permian strata; of these we 
have figured some of the most characteristic forms on Pl. xlii., Cama- 
raphoria’ crumena, fig. 2. C. Humbletonensis, fig. 3, a,b. Strophalosia 
lamellosa, fig. 4, and Productus horridus, fig. 5, a, 6. 
Eight of the Permian species are shown by Mr. Thomas Davidson, 
Mr. J. W. Kirkby and others to be synonyms of Carboniferous fossils ; 
one of them as stated by Mr. Davidson is a recurrent species appearing 
in the Devonian as Spirifera unguicula; in Carboniferous strata as 
Spirifera Uri’, and in the Permian as Spirifera Clannyana. 
The Conchifera are also few and of small size, Monotis (Avicula) 
speluncaria, Pl. xlii., fig. 6. Bakewellia antiqua, fig. 7. Axinus 
truncatus, fig. 8, and Pleurophorus costatus, fig. 9, are some of the most 
frequent fossils. 
The Gasteropoda likewise decrease considerably in number and size 
from those of the Carboniferous Limestone. Zurbo Marcuniensis, fig. 10, 
a-c, and Pleurotomaria antrina, fig. 11,a, 6, are the only examples 
figured. 
Of the CerHaLoropa, a group so abundant in Carboniferous strata, 
one species only, Nautilus Frieslebeni, is recorded. 
The Trrtosrres, a group of Crustacea which commenced in the 
lowest fossiliferous rocks, attaining their maximum development dur- 
ing the Silurian period, decreasing considerably in Devonian deposits, 
and still more in the Carboniferous strata, appears to have entirely died 
out with that formation, no species having yet been discovered in Per- 
mian strata. 
Fossil fish are not unfrequent, more than forty species having been 
described from Permian deposits ; all of them, like those of more an- 
cient strata, belonging to a division called by M. Agassiz, Heterocercal, 
from having their tails unequally lobed like the recent Shark and 
Sturgeon; the vertebral column continuing along the upper caudal 
lobe (see fig. 15, a, p. lvii.). In the Homocercal fish, which include almost 
all the species (about 9,006) living at the present day, the tail-fin is 
either single or unequally divided, and the vertebral column is not 
prolonged into either lobe, as in the herring, mackerel, &c. (see fig. 
15, 6). The fish selected for illustration, Platysomus striatus, Pl. xlii., 
fig. 12, a-c, is a characteristic example of the first named division. 
Most of the genera of fish found in Permian deposits are also known 
in Carboniferous strata; the species are, however, for the most part 
distinct. The prevailing genera are Palaoniscus, Pygopterus, Celacan- 
* Annals and Mag. Nat. Hist., 1862, 
