66 
Case and 
Column of 
Drawers. 
UPPER CAMBRIAN. 

Reference to McCoy’s 
Synopsis: and Figures of Genera. 

Gm 
Gm 

Arca, 
Pl. 1 K, figs. 2, 3, p. 283. 
Nucula levata, 
Pl. 1 K, figs. 4, 5, p. 285. 

Sea Butterflies generally of 
large size. | 

Names and References: Observations, &c. 

Numbers and Localities. 

Ctenodonta Edmondiiformis, McCoy. 
Ctenodonta varicosa, Salter, Siluria, 3rd ed. 
woodcut 39, fig. 4. Mem. Geol. Surv. m1. 
p. 345, woodcut 13, fig. 1, p. 343. 
Cucullella antiqua? Sow. (Siluria, 2nd ed. pl. 
34,.fig. 16). 
Palearca, Hall (Cyrtodonta, Billings. Cypricar- 
dites, Hall). With the general structure of 
Cucullza these ancient bivalves want the 
posterior internal plate, and are closely re- 
lated to Ctenodonta, and have affinity with 
Pterinea. Several species are known at 
Bala, and should be added to the collection. 
PTEROPODA AND HETEROPODA (or 
Nucleobranchiata). 
The Pteropods are among. the Mollusca the 
most simple in structure of the cephalate 
orders. They are also the most ancient. The 
Heteropoda or Nucleobranchs are low down 
in the scale, being nearest like the embryos of 
Gasteropods, 
poda grew to an enormous size in the older 
Palaeozoic times. 
Theca, Morris, 1844. A triangular Pteropod 
shell, with an operculum (Barrande). The 
genus is related to the much smaller living 
genus Creseis, Rang. These were floaters, 
and as such the genus had a very wide 
range in olden time. Such fossils too, not 
being subjected to the full force of local 
elevation, have been usually long lived. 
Theca is found all through the Lower and 
Upper Cambrian to the Devonian epoch. 
| Theca reversa, Salter (7. Forbesii, Hall, not of 
Sharpe, figured in Siluria, 3rd ed. p. 199, 
Foss. 41, fig. 1). Mem. Geol. Surv. Vol. m1. 

p- 353 (woodeut 14, fig. 6, p. 347). 
Both Pteropoda and Hetero- | 

a. 
212, Alt-y-Gader. 
a, 164, Milltir Cerrig 
(milestone), on the Llan- 
wddyn road. The species 
is acommon one at Conway 
falls. 
a. 213, Conway falls. 
in Wales 
Shropshire. 
Common and 

