80 UNIVALVES. — BULLA. 



The next variation of form is discernible in the B.ovum, 

 or poached egg^ of which there are two varieties : the com- 

 mon, from Amboyna, is white without, and yellow with- 

 in j the rarer, from the Friendly Isles, is white without, 

 and pink within. These shells are less beaked and more 

 gibbous than the B. volva, and lead into the following or- 

 bicular species; viz.theB.naucum, B. physis, B. ampulla, 

 &c. These are without teeth, and rather umbilicated. 



The B. terebellum is an exception to the general form 

 of the Bullee, its shape being remarkably long and slen- 

 der, and resembling a lengthened olive. 



Some of the Bullae, as the B. ficus, and B. rapa, arc ve- 

 ry similar to the genus murex : the latter species is es- 

 teemed a rarity ; the former, on the contrary, is common, 

 and very much resembles the shape of a fig. 



The B. zebra, B. bifasciata, B. achatina, and other simi- 

 lar species, are land shells 5 in form, they are nearly al- 

 lied to the genus helix. It is remarkable, that the ani- 

 mals which inhabit them are oviparous. The reverse va- 

 rieties, that is to say, those having their whirls or spires 

 twisted contrary to the usual direction, and having, at the 

 same time, their mouths placed on the opposite side, are 

 highly valued. The B. purpurea inhabits Africa, and is 

 found in rice fields. 



Some species of this genus are remarkable for the brit- 

 tleness and lightness of their shells ; such are the B. velum, 

 B. vesica, &c. 



The inhabitant of the B. lignaria, and, in all probabi- 

 lity, of many other species, is furnished with an organ call- 

 ed a gizzard, of a testaceous nature. 



The different species of this genus are to be found in 

 the Mediterranean, African, American, Indian, European, 

 and Northern seas. 



