152 CLASS III. GASTEROPODA. ORDER VII. PECTINIBRANCHIATA. 
not being of the same tubular construction, and in not having the margin 
of the aperture reflected. 
D’Orbigny introduces a subgenus with the name of Rissoina for such 
as have the margin of the aperture sinuated or obsoletely canaliculated. 
The shell of Rissoa may be described as being small, turriculated, and 
acuminated at the apex ; the aperture is oval, nearly orbicular, and entire, 
somewhat triangular at the upper part, and slightly spread out at the 
lower; the margin is thickened, not reflected, and somewhat canalicu- 
lated near the columella. The operculum is horny. 
Examples. 
Pl. CCVIII. Fig.-1. (fossil.) 
Rissoa reticuLata, Philippi, Enum. Moll. Sicil., p. 156. pl. 10. f. 14. 
Pl. CCVII. Fig. 2. 
RissoA DEFORMIS, Sowerby, Genera of Shells, No. 40. 
2? D’Orbigny. 
Rissoina 
Pl. CCVII. Fig. 3. 
Rissoa spirata, Sowerby, Genera of Shells, No. 40. 
Pl. CCVIII. Fig. 4. 
Rissoa acicuLa, Sowerby, Genera of Shells, No. 40. 
EULIMA, Risso. 
Testa parva, turriculata, acuminata, polita, anfractibus plurimis, versus 
apicem szpé contortis ; seu umbilico profundo, seu columella solida 
umbilico nullo; apertura ovata, superné acuté angulata, inferné 
vel angulata, vel rotundata, labro subincrassato, varices obsoletos 
interdum formante. Operculum corneum, tenue, nucleo antico. 
