162 CLASS III. GASTEROPODA. ORDER VII. PECTINIBRANCHIATA. 
coid, generally shining, and convex on both sides, the spire being very 
short, and the under surface of the shell hard and callous, without any 
trace of an umbilicus; the aperture is semilunar, with the margins dis- 
joined, and the lip simple and acute. The operculum, which is of an 
orbicular form, is horny and spiral. 
Examples. 
Pl. CCXVI. Fig. 1. 
RoreLLa MONILIFERA, Lamarck, Anim. sans vert., vol. vii. p.8. Gualt. 
Tests pl-Go: i. E: 
Pl. CCXVI. Fig. 2. 
RoreLLA vestiarta, Sowerby, Genera of Shells, No. 14. Favanne, 
Conch., pl. 12. f. G. 
Trochus vestiarius, Linnzeus. 
Rotella lineolata, Lamarck. 
Pl. CCXVI. Fig. 3. 
(Variety of the same, magnified.) 
TROCHUS, Linneus. 
Testa conica, pyramidalis, subtis planiuscula; spira elaté, anfractibus 
depressis, peripheria plus minusve acuta; columella arcuata, ad 
basem szepé truncata, seu dentata, nonnunquam crenata; margini- 
bus disjunctis, labro acuto, vel simplici, vel denticulato. Operculum 
hune corneum, nune calcareum. 
In contemplating the great theory of Nature it is everywhere manifest 
that she cannot be made strictly subject to arbitrary division ; her move- 
ments and developments exhibit such an exhaustless love of variety, that 
in their multitude of forms and modifications an easy affinity is established 
between the highest and the lowest state of organization ; between man 
