PTEROPODA 



HyALjEA. Fig. 1. 



Testa subglobosa, tenuis, hyalina, fragillima, dorso superne 

 subrostrato, infra tridentato, dente centrali validiore, 

 apice pervio ; ventre superne gibboso, breviore, aper- 

 tura lineari, supra- ventrali, ad lateres continuL 



The Hyalseae are in general nearly globular, very thin, 

 transparent and brittle ; they may be regarded as consti- 

 tuted of two parts, united together at the lower edge, one 

 part being apparently dorsal, larger than the other, re- 

 flected and subrostrated at the upper end, tricuspidate 

 and united to the ventral portion by the edge below; the 

 central tooth being the longest, and open at the end; the 

 other part appears to be ventral, which is shorter and 

 gibbous above; the aperture is linear, continuing between 

 the dorsal and ventral parts at the upper end, and on 

 both sides. 



Occurs in a fossil state in Sicily. 



Cleodora. Fig. 2. 



Testa inverse pyramidalis, hyalina, incolorata, tenuissima, 

 fragillima, dorso superne rostrato, infra acuminato, 

 ventre supern^ breviore, lateribus acuminatis, aper- 

 ture magna, supra-ventrali, ad lateres coarctata. 



The Cleodorae differ from the Hyalaeoe principally in the 

 form of their shells; they are even thinner, more trans- 

 parent, more brittle and altogether more delicate; and 

 they have the appearance of the thinnest and most trans- 

 parent glass. 



Shell inversely pyramidal, transparent, colourless, 

 extremely thin and fragile, dorsal portion rostrated at 

 the upper extremity, and acuminated at the lower; ven- 

 tral portion shorter above, angular and acuminated on 

 the sides ; aperture large, dilated in the middle, smaller 

 and contracted on the sides, placed above between the 

 dorsal and ventral portions. 



