36 CLASS III. GASTEROPODA. ORDER III. CERVICOBRANCHIATA. 
The shell of Pileopsis is described as being cap-shaped, obliquely coni- 
cal, and covered with a soft velvety epidermis ; the vertex is crooked, 
and the aperture is large and rotundately elliptic, exhibiting two lateral 
muscular impressions, which are connate posteriorly, and separately 
rounded anteriorly. 
Example. 
Pl. CXLVI. Fig. 1 and 2. 
Pitzopsis uNGARicA, Lamarck, Anim. sans vert., new edit., vol. vu. 
p. 609. Pennant, Zool. Brit., pl. 93. f. 1. 
Patella ungarica, Linneus. 
Capulus ungaricus, De Montford. Sowerby. 
Family 3. MACROSTOMATA. 
Testa paululum convoluta, spira brevi; serie foraminum nonnunquam 
perforata ; interdum intra pallio plus minusve celata; apertura am- 
plissima. 
The Macrostomata or open-mouth Gasteropoda, which Lamarck first 
distinguished by the title of ‘‘ Les Stomatacées,” are placed here on ac- 
count of their cervicobranchiate affinity with the Capulacea; they are 
moreover the first of the class whose shells exhibit an indication of the 
spiral growth. Lamarck, who did not devote that particular attention 
which is now given to the nature and position of the breathing organs, 
placed them after the Neritacea in consequence of the affinity that exists 
between the Natice and the Sigareti, so far, at least, as regards the fact of 
their shells being almost entirely concealed within the mantle. It must 
be allowed, however, that although the respiratory cavity in all the Ma- 
crostomata is cervical, a considerable difference may be observed in the 
arrangement of it; as between that of Haliotis and Sigaretus, for ex- 
ample. De Blainville and Deshayes, both of whom have entered more 
minutely than most authors into the nature and arrangement of the 
