FAMILY 6. TURBINACEA. 161 
Pl. CCXV. Fig. 6. 
Puorus Inpicus, Nobis, Proceedings Zool. Soc., 1841. 
Trochus Indicus, Wagner, Supp. to Chemnitz, pl. 229. f. 4062. a, b. 
Pl. CCXV. Fig. 7. 
Puorus CALCULIFERUS, Nobis, Proceedings Zool. Soc., 1841. 
S 5) 
Pl. CCXV. Fig. 9 and 10. 
Puorvus Exutus, Nobis, Proceedings Zool. Soc , 1841. 
ROTELLA, Lamarck. 
Testa orbicularis, subdiscoidea, plerumque nitida, utrinque convexa, 
spira brevissima, facie inferna callosd, umbilico nullo; apertura 
semilunari, marginibus disjunctis, labro simplici, acuto, basi sub- 
prominente. Operculum corneum, spirale, orbiculare. 
The Linnean Trochus vestiarius, with the few species allied to it, a 
small group of mollusks distinguished by the equi-convexity of their 
shells, were selected by Lamarck for the formation of this genus. They 
had been already set apart by De Montford under the generic title of 
Pitonillus ; but as this author had confounded certain species of Helicine 
with them, attracted by a slight similitude in the formation of their 
shells, without regarding the important difference in their organization 
and habits, the name of Pitonillus was very properly abandoned for that 
of Rotella in order to escape confusion. De Blainville, considering the 
Rotella merely as a sectional subdivision of the genus Trochus, for a long 
time refused to acknowledge the rank that was assigned to them by La- 
marck and his numerous followers; he however subsequently admitted 
the propriety of it, and now there are not two opinions on the subject. 
The shell of Rotella may be described as being orbicular, nearly dis- 
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