166 



75. Euomphalus. An involute and rather discoidal uni- 

 valve ; the spire depressed ; concave beneath, or largely um- 

 bilicated ; aperture mostly angular. Fossil. PL v. fig. 22. 



76. Janthina. A subglobose univalve ; the opening 

 triangular, with an angular sinus on the right edge. Re- 

 cent. PL v. fig. 23. 



77. Trochus. A conical univalve ; the opening almost 

 quadrangular, transversely depressed; the axis oblique on 

 the plane of the base. PL v. fig. 24. 



78. Solarium. A conical univalve, with an open um- 

 bilicus underneath ; the inner edges of the whirls crenu- 

 lated; the opening nearly quadrangular. Recent and 

 fossil. PL v. fig. 25. 



Multilocular Univalves. 



M. Denys de Montfort, author of an interesting and im- 

 portant work, Conchyliologie Systematique, has, with much 

 careful discrimination, separated into different genera the 

 multilocular univalves ; the microscopic shells into sixty ; and 

 those which are within the power of the naked eye, being those 

 which had been included in nautilus, ammonites, belemnites, 

 orthoceratites, spirula, scaphites, nummulites, and siderolites, 

 into forty genera ; forming almost every shell, marked by a 

 slight difference, into a distinct genus. These separations, 

 although, perhaps, founded on accurate discrimination, ap- 

 pear to be too frequent ; and their multiplicity bears too 

 much on the memory, and deprives it of the aid which it 

 seeks to derive from classification. These observations are 

 applicable only, perhaps, to the larger kinds ; for, as to the 

 microscopic shells, the eccentricity of their forms, their vast 

 variety, and the peculiarity of character which mark their 

 ornaments, must render their classification a very difficult 

 task; every different shell appearing to repel all association. 

 A more intimate knowledge of their nature and charac- 



