DESCRIPTIVE REMARKS. lv 
equivalents of the true Old Red Sandstone, at Kiltorcan, is the large bi- 
valve before alluded to Anodonta Jukesii Forbes ; this shell is figured on 
Plate 31, fig. 5, reduced to two-thirds of natural size ; its close alliance 
with the large fresh water mussel, Anodon, cygneus of our lakes, its 
association with numerous land plants and fish of a type analogous to 
those inhabiting inland lakes and rivers, favour the theory of the fresh 
water origin of the Old Red Sandstone. 
Small bivalved Carapaces of Crustacea belonging to the order 
Puyttoropa, named Estheria membranacea (Plate 32, fig. 5, a, 8, ec), 
have been found abundantly in the central or Caithness flags near 
Wick. Another form Beyrichia Kledeni, belonging to the order Os- 
tracoda has also been met with in the Old Red Sandstone of Shrop- 
shire.* 
Crustacea of the Evryprerrpa, an order which includes some of 
the largest examples of the class,}| commencing in the Uppermost 
Silurian, are also found in the Basement beds of the Old Red Sand- 
stone, represented by one of the largest species, Pterygotus anglicus, of 
which figures of some of the parts, reduced to one-fourth the natural 
size, is given on Plate 32, figs. 7, a—-e, from the monograph by Messrs. 
Huxley and Salter.t This species is found in strata called the Perth 
and Forfarshire Paving Stones, at Balruddery Den, Perthshire. A 
second species of Pterygotus occurs plentifully in the Yellow Sandstone 
of Dura Den. 
These remarkable Crustacea, allied to the recent King Crab, X¢pho- 
sura, and the Copepoda, are composed of a number of moveable seg- 
ments, usually about eleven or twelve; the anterior portion (carapace 
or head), being square shaped, and provided with a pair of eyes, gene- 
rally at the upper edge, but in some species more central; to the under 
part of the head are attached three or four pair of moveable swimming 
feet and antenne, the latter armed with powerful pincers as in the 
lobster ; the tail, or fe/son, usually terminates in a pointed spine, but 
is sometimes lobed or rounded; the surface of the integument is orna- 
mented with semicircular plications or markings of a half moon shape. 
Figure 14 is a restored outline of Pterygotus, with a recent allied 
crustacean, Sapphirina, the former considerably reduced in size, from 
the monograph by Mr. Woodward, Paleontological Society, 1865, Plate 
vili., fig. 1, and Plate ix., fig. 4. 
* Chart of Fossil Crustacea, by Salter and Woodward, p. 19, fig. 47. 
+ Descriptive remarks, ante, p. xlvii., &e 
t Memoirs of the Geological Survey of the United Kingdom, Monograph 1, 1859. 
