Scissurella laevigata, coslata, and decussata. 257 



Found on the Coasts of the Mediterranean, among the Fuci and 

 Ceramia, where it is very rare. Length two millim. 



Shell oval, smooth, white, translucent, thin, fragile, apex de- 

 pressed, volutions marked only by the lines of growth, without 

 the ribs or grooves which characterize the three following species. 

 The space between the two edges of the obliterated part of the 

 slit, (each of which edges forms a ridge) is smooth, without trans- 

 verse lines, and obliterated to within a short distance of the edge 

 of the aperture, the umbilicus has several very fine circular striae ; 

 the aperture is oval, longer than it is broad; peristome sharp- 

 edged. 



Species 2. 



Scissurella costala, testa ovali, alba, translucente, fragili, apice 

 depresso, anfractibus tribus, superne costis transversis, elevatis, 

 distantibus ; infra costis prominentioribus, fere acutis. 



Found in the same situations as the last. Length one millim. 



Shell oval, white, translucent, fragile ; apex depressed, volu- 

 tions three, the upper part furnished with transverse, elevated, dis- 

 tant ribs ; ribs beneath more prominent, and almost sharp-edged. 

 The intercostal spaces are nearly smooth. The two edges of the 

 slit form two ridges, the interval of which, in the obliterated part, 

 is strongly marked with close transverse lines ; umbilicus sur- 

 rounded by circular striae ; aperture nearly quadrangular ; peris- 

 tome sharp-edged. 



Species 3. 



Scissurella decussata, testa ovali, tenui, fragili, decussata; apice 

 depresso ; anfractibus tribus, costis supra et infra, transversis, nu- 

 merosis. 



Found in the Fossil sand of Castel-Arquato in Piacenza. 

 Length one millim. 



Shell oval, thin, brittle, decussated, apex depressed, volutions 

 three, marked above and below with numerous transverse ribs or 

 salient grooves, the intercostal spaces have close-set, deep, longi- 

 tudinal striae ; the space comprised between the two raised edges 

 of the slit is marked, in its obliterated part, by broad, distant 

 grooves. 





