MOLLUSCS. 



305 



forms bv an upper jaw composed of either one or three j)ieces ; in others, no upper jaw 

 is present. 



The generative apparatus is rather complex and affords good systematic characters. 

 The most noticeable feature is that from the ovo- 

 testis a single duct proceeds, which afterward 

 divides into two tubes, one connecting with 

 the male, the other with the female copulatory 

 organs. In the Helicid» peculiar crystalline, 

 fluted, chitinous, or calcified rods or darts {sjyic- 

 uhi amoris) are formed, the functions of which 

 are still problematical. 



The eggs are laid in moist places, in damp 

 earth, under dead leaves, etc. ; or, by the aquatic 

 species, in the water. Those of Limncea and 

 Planorbis are easily studied during their devel- 

 o]iment. In Umax, — the eggs of which are 

 laid separately, each one resembling a drop of 

 dew — when the embryo is far along in its de- 

 velopment, a jieculiar pulsating sac is formed 

 in the middle of the foot, the function of whicli 

 is as yet uidvnown. 



Sub-Okder I. — Basommatophora. 



The position of the eyes affords a good char- j-io. 348. -Embryo of Umax; d, yolk; e, eve; 



acter for a division of the Pulmonata into two {{^,1^:^^^^:^!^'^;^^^^^^::^ 

 sub-orders. In the present group the visual granules.. 



organs are seated at the base of the solid, contractile feelers; the velum of the larva is 

 retained in the adult ; and the male and female generative apertures are separate and 

 [ilaced on the right side of the neck. Most of the members of the sub-order are aquatic 

 in habits, though some lead more or less terrestrial lives. 



The family Amphibolid.k, which occurs only in the New Zealand seas, serves to 

 connect the pulinonates with the opisthobranchs. They live in the salt marshes, 

 where the water is at least brackish, but are partially aerial in tlieir respiration, although 

 rudimentary gills are present. The shells are closed by a horny operculum. In 

 these two features the Amphibolidse differ from all other pulinonates. The shell is 

 spiral and thick, the spire sliort and the wliorls shouldered. The native New Zea- 

 landers eat the animal. 



The families G.vijixid.e and Siphonarid.k embrace together about a hundred 

 species of limpet-like pulmonates, with sliell and habits nearly like Acmrnu and Patella. 

 No species are found on the east coast of the United States. 



Concerning the Aubiculid^ more can be said. The animals are mostly tropical; 

 still several small species are found even in the northern states. The spiral shell is us- 

 ually thick and solid, and covered with an epidermis. The spire is short, the body 

 whorl large, and the outer lip is thick and frequently armed interiorly with teetli 

 which considerably contract the aperture. Simil.ar teeth are found on the columellar 

 lij). The respiratory pore is ]iosterior, and the male and female reproductive organs are 

 widely separated. Tlie moutli is armed with a horny jaw. 

 VOL. I. —20 



