158 CLASS III. GASTEROPODA. ORDER VII. PECTINIBRANCHIATA, 
Pl. CCXII. Fig. 12. 
DeLpuinuta atrata, Nobis, Proceedings Zool. Soc., 1842. 
Delphinus atratus, Chemnitz. 
SOLARIUM, Lamarck. 
Testa circularis, subdiscoidea, depresso-conica, anfractibus plurimis, 
peripheriaé acuta, in spiram planiusculam convolutis, umbilicum 
spiralem, amplissimum formantibus, anfractuum margine interno 
crenato; apertura trapeziformi, labro simplici acuto. Operculum 
corneum, subspirale. 
The genus Solarium is one that was introduced by Lamarck in distri- 
buting the Linnean Trochi, and it has been adopted without alteration 
by all succeeding writers. There are few mollusks, indeed, whose shells 
present a more distinct peculiarity of structure than those of the Sola- 
ria; they are all of a circular depressed form, and are composed of a 
number of slowly enlarging whorls, resting one upon the other in such 
exact order, that they form on the inner side a wide, open, spiral umbi- 
licus. The progress of the whorls is, in fact, marked with such exceed- 
ing regularity of growth, that upon looking into the umbilicus before a 
strong light, it exhibits almost a perspective illusion. 
The shell of Solartum may be further described as being of the form of 
a flat, depressed cone, consisting of a number of whorls, which are sharp 
round the outer edge, whilst the inner edge is always crenated ; the aper- 
ture is trapeziform, and the lip is simple and acute. The operculum is 
horny and somewhat spiral. 
Examples. 
Pl. CCXIII. 
SoLariuM PERSPECTIVUM, Lamarck, Anim. sans vert., vol. vii. p.3. En- 
cyclopédie Méthodique, pl. 446. f. 1. a, 6. 
Trochus perspectivus, Linnzeus. 
