THE HIGHLAND BORDER ROCKS OF THE ABERFOYLE DISTRICT. 
191 
crushed from side to side ; a pair of cardinal scars can be discerned near the apex, 
and a median septum is faintly seen. Fine concentric lines of growth are shown 
towards the anterior margin of the shell. This species occurs in the Upper Cambrian 
of Shropshire * and the Malvern Hills.f 
Genus Siphonotreta, de Yerneuil. 
Siphonotreta aff. micula, M‘Coy. — A photograph and a drawing of a specimen 
are shown in figs. 17 and 17a. It is the exterior of the ventral valve broken across. 
The characteristic punctations are seen on the surface and concentric lines of growth. 
S. micula has been recorded from the Ordovician of Wales and the South of 
Scotland. J 
Siphonotreta aff. scotica, Dav. — The specimen shown in figs. 18 and 18a resembles 
very closely S. scotica as figured and described by Davidson. § The fossil is a cast 
of the interior of the ventral valve with a part of the rim of the exterior of the 
valve. Concentric lines of growth are faintly seen, and small pits or dots at places. 
Around the rim, fringes of spines are seen to take their rise from the shell. S. scotica 
has been obtained from the Llandeilo Beds of the Girvan district, South of 
Scotland. || 
Genus ? Schiz ambon, Walcott. 
Another form appears to belong to the family Siphonotretidse, but it differs from 
Siphonotreta, and seems to bear a closer resemblance to Schizamhon as figured by 
WalcottA Figs. 19 and 19a show the interior of the dorsal valve, in which the 
septum and muscle scars can be discerned. Faint traces of spines can be detected. 
It has not been found possible to determine the species. Hitherto this genus has 
been recorded only from the Upper Cambrian and Ordovician of Russia and 
North America. ## 
IV. PHYLl6cARIDA (LEPTOSTRACA). 
Remains of bivalved phyllocarid crustaceans are found which appear to be allied 
to the genera Lingulocaris, Salter, Ceratiocaris, M £ Coy, and Peltocaris, Salter. 
These are all Upper Cambrian and Ordovician genera. 
The best preserved specimen is shown on Plate II, fig. 3. Dr Peach has 
supplied a drawing (Plate II, fig. 3a) of this specimen and a description from an ex- 
amination of the specimen figured and of its counterpart (not figured). He says : — 
“This is a bivalved phyllocarid allied to the Ordovician Ceratiocaris. It shows' 
the exterior of the left valve of the carapace, and also traces of five thoracic and six 
* Calloway, Quart. Jour. Geol. Soc., vol. xxxiii, p. 669, 1877. 
t Matley, Qu&rt. Jour. Geol. Soc., vol. lviii, p. 143, 1902. 
I Davidson, Brit. Fossil Brack. (Pal. Soc.), vol. iii, pt. 7, p. 77. 
§ Brit. Silurian Brack., Suppl., p. 217, pi. xvi, figs. 31-33. || Ibid., p. 217. 
IT Gamb. Brack. (U.S. Geol. Survey Monog., vol. li, pt. 2), pi. lxxxiv, 1912. ** Ibid., pt. 1, p. 104. 
TRANS. ROY. SOC. EDIN., YOL. LII, PART I (NO. 9). 30 
