64 
UPPER CAMBRIAN. 


Case and 
Column of 
Drawers. 
Reference to McCov’s 
Synopsis: and Figures of Genera. 

Names and References; Observations, &c. 
Numbers and Localities. 



LL. quinquecostata. 
Pl. 1 4, fig. 31, 32. 
p. 239. 
do. 
Pl. 14, fig. 44, p. 239. 
do. 
PL. 14, fig. 30, p. 236. 
Pl. 1 4, fig. 40, p. 239. 

Ordinary Bivalve shells. 

Leptena transversalis, var. undulata, Salter, 
Mem, Geol. Sury. m1. p. 276. Catal. Mus. 
Pract. Geol. p. 9, often mistaken for L. quin- 
quecostata, but differs in its undulated sur- 
face, and many, instead of 3—5 strong ribs. 
Leptena sericea, Sow. (Siluria, 2nd ed. pl. 5, 
fig. 14). Extremely common, It has a fine 
even surface closely striated. The muscular 
sears are short for the genus. 
Leptzna sericea, var. « rhombica, McCoy, prob- 
ably not of Phillips. 
Leptena, do. (internal cast, quoted in p. 237). 
Leptena tenuissimestriata is a bad species, 
made up of L. sericea and L. transversalis. 
See Lower Bala group. 
Leptena, new sp. fine striz, prominent beak. 
Leptena quinquecostata, Orthis, McCoy (Sil. 
Foss. Ireland, pl. 3, fig. 8). 
Leptena tenuicincta, McCoy (An. Nat. Hist. 
2 ser. 8, p. 401). A species much longer 
than wide. Very common in §8. Wales 
(Bala limestone) with large long muscles. 
Lamellibranchiata or Conchifera. 
(Pleuroconcha—Acephala, of various authors). 
Prof. Phillips has suggested (Mem. Geol. Surv. 
Vol. 11. Pt. 1, p. 263— 275), that the ear- 
liest Lamellibranchiata (not Brachiopods) 
known, and these do not descend further 
than the Arenig or Skiddaw group, are 
everywhere referable to the Modiola and 
Arca groups, notably to the latter. These 
groups stand at the junction, so to speak, of 
the Dimyaria and Monomyaria groups. The 
fact is worthy of notice, in reference to any 
theory of development of organic forms. 


Every possible locality in 
Bala rocks both Middle and 
Upper, N. and 8S. Wales. 
Pont-y-Glyn, Diffwys, Cor- 
wen; Glyn Ceiriog; Pen- 
machno; Capel Currig; Bet- 
tws; Pwllheli; Llanfyllin; 
Llanfechan ; Gaerfawr, 
Guilsfield, &c., Horderley. 
b. 256, Gelligrin; Bala; a. 
242, Alt-yr-Anker, Meifod. 
b. 254, Llandrillo. 
Bower Bank, Dent. 
b. 253, Glenquhaple, 34 
miles S. of Girvan. 
b. 252, Cefn Grugos, Llan- 
fyllin; Keisley, Dufton 
(Prof. Harkness). ' 
