i8 



INTERMEDIATE FORMS 



have yet never become, in respect of habitat, genuine fresli- 

 water species. Like Potamicles, they haunt salt niarslies, man- 

 grove swamps, and the region 

 about high-water mark. In some 

 cases (Otina, Melam^ius, Prdi'pcs) 

 they live on rocks which are 

 moistened, or even bathed l)y the 

 spray, in others (Cassidula, Auri- 

 cula) they are immersed in some 

 depth of brackish water at high 

 tide, in others again {Scarahus) 

 they are more definitely terres- 

 trial, and live under dead leaves 

 in woods at some little distance 

 Fig. 1 4. -Exaoipies of the A uricuiidae . ^om water. I ndeed one genus of 



A, Auriada Judae Lam., Borneo ; dindnutivC size {Cciryclliuni) haS 



B, Scarabus Lessoni Blaiuv., E. i.i ^ -i -i ,-, ■ ^ 



Indies ; c, Cassidula musteUna Completely abandoned the neigh- 



Desh., N. Zealand ; D, Melampus l.ourhood of the sca, and inhal)its 



castaneus Miihlf., S. Pacific ; E, 



Pedipes quadridcns Pfr., Jamaica. SWanipy ground almost all OVer 



the world. 

 To this same section Gehydrophila have been assigned two 

 remarkable forms of air-breathing "limpet," Siphonaria and 

 Gadinia (see page 151), and the aberrant Amphibola, a unique 

 instance of a true operculated pulmonate. Sijiho- 

 7iaria possesses a pulmonary cavity as well as 

 a gill, while Gadinia and Ampliihola are ex- 

 clusively air-breathing. Si2)honaria lives on 

 rocks at or above high -water mark, Gadinia 

 between tide marks, Amphibola (Fig. 15) in 

 brackish water at the estuaries of rivers, half 

 buried in the sand. There can be little doubt 

 that all these are marine forms which are 

 gradually becoming accustomed to a terrestrial 

 existence. In Gadinia and Amphibola the pro- 

 cess is so far complete that they have ex- 

 changed gills for a pulmonary cavity, while in Sip)1ionaria 

 we have an intermediate stage in whicli both organs exist 

 together. A curious parallel to this is found in the case of 

 Amjjullaria, which is furnished with two gills and a pulmonary 

 chamber, and breatlies indifferently air and water. It is a little 



Fig. 15. — An example 

 of Amphibola {av- 

 ellana Cheni.), the 

 only true Pulmo- 

 nate which pos- 

 sesses an opercu- 

 lum. 



