208 CLASS IlI. GASTEROPODA. ORDER VII. PECTINIBRANCHIATA. 
those of the Harpe, where they are remarkably numerous ; a few others 
occasionally exhibit a rudimentary one, or more. 
The greater portion of the Purpurifera are included by De Blainville in 
his family of the Entomostomata, agreeing as nearly as possible with the 
plan of Lamarck here followed ; one genus, however, Columbella, has been 
variously arranged by authors. Lamarck placed it with the Columellata, 
as being allied to the Mitre; De Blainville with the Canalifera, as being 
allied to the Turbinelle ; and Deshayes and Gray with the Purpurifera, as 
being allied to the Ricinule ; we think the last of these arrangements 
undoubtedly the most entitled to consideration. The genera Ancillaria 
and Oliva, which are here referred to this family after Gray, were ar- 
ranged with the Convoluta by Lamarck, and with the Columellata by 
Deshayes. 
We include twenty genera in this family, as follows : 
CasSIDARIA. ‘TRICHOTROPIS. 
OnNIsciA. Maci.uvs. 
Cassis. LEPTOCONCHUS. 
RIcINULA. Buccrnum. 
CoLUMBELLA. Nassa. 
PuRPURA. PLANAXIS. 
Monoceros. Epurna. 
CoNCHOLEPAS. ANCILLARIA. 
Harpa. Ouiva 
Do.ium. TEREBRA. 
CASSIDARIA, Lamarck. 
Testa ovoidea, anfractu ultimo ventricoso, ad basem attenuata, in cana- 
lem curvum, posticé ascendentem, desinens ; apertura longitudinali, 
inferné angustata; labro columellari levi, latissimé effuso ; labro 
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