58 CRETACEOUS GASTROPODA 
Formations.—Trichinopoly and Arrialoor groups. In France Cyprea (Ovula) 
Kayei is quoted from D’Orbigny’s Senonien, or the White Chalk. 
VIII. ERATO, Risso. 1826. 
Er. testa ovali, convoluta: spira conspicua, brevi; ultimo anfractu plus minusve 
pyriform, maximo; apertura angusta, antice atque postice emarginata, sew sub- 
canaliculata, labro intus denticulato, labio antice plicose-dentato, postice edentulo. 
H. and A. Adams, Chenu, and others separate the genus Erato from Cyprea 
altogether, and place it with Marginella, &c., in the family Marerwerrips. Even 
Reeve in his latest monograph of this genus (Conch. Icon., 1865) says :—‘ Hrato is 
a form of Marginella, in which the columella, like the lip, is not sculptured until 
it arrives at maturity.” This is certainly in conformity with Cyprea, and not with 
Marginelia, with which also the enamel covering of the shell does not agree. 
Hornes (Foss. Moll. Wien. I, p. 77) pointed out very correctly the differences 
between the shells of Hrato and Marginella. The former, he says, does not possess 
any actual plicee on the columellar margin (as Warginella very distinctly does), but 
only somewhat elongated teeth, for which the term ‘ obsolete plicata’ has been used. 
Hornes further drew attention to the great similarity of the shell of Hrato with that 
of a young, or rather not full-grown, Cyprea; indeed, in comparing, for instance, 
specimens of Cyprea asellus or any allied species,—before they are quite full grown 
and when the enamel covering is not yet very thickly secreted, the spire somewhat 
conspicuous, and the teeth of the inner lip not much developed,—the similarity of 
such specimens to shells of Hrato is so striking, that nobody would hesitate to 
regard rato merely as a form of Cyprea. It appears as if the animals of 
the former had been by some cause or other stopped in the progressive development 
of their shell, while Cyprea made a step farther and secreted so much enamel as to 
cover the entire spire, by which character alone some species of Zwponia differ from 
Erato. 
In my revision of the Gastropoda of the Alpine Gosau formation I have observed, 
that the Cypree of the older formations (not beyond the cretaceous) show very — 
often an elevated spire, and that the margins of their aperture have often a finer 
dentition than in living species. Overlooking the deficient state of preservation, 
which makes the true characters of Cyprea often rather obliterate, the elevation of 
the spire in several eocene and cretaceous species is certainly not always accidental, 
and seems actually to indicate a certain state of imperfection in the development. 
T do not mean to convey by this remark, that the cretaceous or eocene species with 
conspicuous spire ought to be referred to Erato on account of this single character 
alone; but when the surface of the shell, as far as can be distinctly observed, 
appears quite perfect, not enveloped by the callosity of the last volution, and when 
the middle and posterior portions of the inner lip do not show a trace of dentition, 
as in the species we are about to describe here, there seems to be a necessity to refer 
the same to Hrato rather than to Cyprea. The single objection which could he 
