UPPER CAMBRIAN. 



Names and References; Observations, &c. 





36 
Beant Reference to McCoy’s 
Drawers.| Synopsis: and Figures of Genera. 
Gk 
L. tenwissimestriata. 
Gk PL 15, f. 44, p. 239. 
p- 237. 
Gk 
G 
G 
Gk 
Gk 

Trochus helicites, p. 297. 


Strophomena, sp. with distant radiating ribs. 
Leptena, Dalman, Salter, Davidson, ina stricter 
sense than used by McCoy. Valves involute, 
muscular impressions greatly elongated. See 
Wenlock List, postea. 
Leptena sericea, Sowerby. Siluria, 2nd ed. 
pl. 5, fig. 14. The commonest of all shells 
in British Upper Cambrian, apparently 
rare out of Britain, 
Leptena, sp. A pretty species with wavy or- 
naments between the ridges, 
Lamellibranchiata (ordinary bivalves) are not 
uncommon in sundry portions of the Llan- 
deilo flags—but none are yet in the collec- 
tion. They abound much more in Middle 
and Upper Bala rocks, in all countries. 
The student may be reminded of the essential 
difference between the Lamellibranchiate 
and Brachiopod shells, by keeping in mind 
that the shells of the former are placed 
laterally, and are unequal on each side of 
the umbo, in the latter they are dorsal and 
ventral, and the umbo is truly central. 
The dorsal valve is really the analogue of 
the foot of the Lamellibranch. (Salter.) 
Mollusca Gasteropoda. 
Univalves, of a few types only, are common 
in Lower Bala rocks. 
Murchisonia (Hormotoma) angustata, Hall, Pal. 
N. York, t. 10, fig. 2. The beaded whorled 
species (Hormotoma, Salter), are common in 
Bala rocks, especially in America. 
Pleurotomaria, sp. 
Raphistoma zqualis, Salter. Siluria, 2nd ed. 
woodcut foss. 37, fig. 2 (R. qualteriata, Mem. 
Geol. Surv. Vol. 11. p. 271). A common genus 
in the Bala group—fiat discoid shells, 

Numbers and Localities. 

Bugon, Knockdollian, Ayr- 
shire. 
a. 94, Llandeilo. 
a. 92, Colmonel, on the 
Stinchar, Ayrshire. 
a.93, Bugon, Knockdollian, 
Ayrshire. 
Same locality. 
a. 95, Llandeilo. 
