"The family Semi-phyllidiana contains
| Pleurobranchus. | |
| Umbella | Patella. |
"The Umbella shell is flat and white, and is sometimes four inches in diameter. It is common in the Isle of France: there is another from the Mediterranean.
"Calyptracea is a larger family: it has many genera taken from Patella:
| Parmorphorus, | Thracian-shield. | |
| Emarginula, |  | Patella. |
| Fissurella, | ||
| Pileopsis, | ||
| Calyptræa, | ||
| Crepidula, | ||
| Ancylus, |
FISSURELLA.
PILEOPSIS.
BULLA.
Parmophorus is found in the seas of New Holland and New Zealand. The margin of the next genus is distinguished by a slit: the shell is conic. ([Plate 3.]) Fissurella has the top of the shell perforated; it is called the key-hole limpet, from the shape of the aperture. Pileopsis is obliquely conic. It was with this division that the curious Hipponyx ranked.