532 MOLLUSCA 



H. rufescens Swainson. Red Abalone. Shell large and thick, 23 

 cm. long, 18 cm. wide, brick red in color outside and pinkish or green- 

 ish inside; 3 or 4 perforations: California, south of Cape Mendocino; 

 common. 



H. fulgens Philippi. Green Abalone (Fig. 824). Shell thin, 15 

 cm. long, iridescent gi'een in color; about 6 perforations: California, 

 south of Monterey. 



H. cracherodi Leach. Black Abalone. Shell 12 cm. long, 10 cm. 

 wide, with 8 perforations, black outside: common south of the Farallone 

 Islands. 



Subdivision 2. AZYGOBRANCHIATA. 



But 1 ctenidium (Fig. 821); shell usually with an elevated spire:* 



marine, fresh-water, and terrestrial; 11 families. 



Key to the families of AzygohrancMata here described: 



ax Animals marine. 

 6i Operculum horny ; shell conical 1. Trochidae 



62 Operculum calcareous. 



Ci Spire not very small 2. Turbinidae 



d Spire very small 3. Nebitidae 



a. Animals terrestrial or in fresh water. 



hi Spire very small 3. Neritidae 



6j Spire not very small 4. Helicinidae 



Family 1. TROCHIDAE. 



Shell usually conical, multispiral, with a flattened base, pearly 



inside ; operculum horny, multispiral ; snout short ; eyes on stalks at 



outer base of the long tentacles, and fringed lobes present on the head 



and foot: about 20 genera and over 1,000 species, all marine. 



Key to the genera of Trochidae here described: 



-^^ Oi Shell pyramidal. 



y^^^^^^c &i Umbilical indentation present 1. Trochus 



^^^^^^^K &2 Without such indentation 2. Calliostoma 



(f^T^^^^ «a Shell conical or globose 3. Margarita 



^5^^^^^^ 1. Trochus L. Shell pyramidal, with a flat base 



Fig. 825— Cal- ^^d flattened whorls; aperture small, oblique, pearly, 



K^jR^ge^rsr^*^ • with a thin outer lip; umbilicus indented: 250 species, 



cosmopolitan, many with beautiful shells. 



T. niloticus L. Shell 7.5 cm. long ; 9 cm. wide ; thick, smooth, white, 



with brownish markings : Indian Ocean ; often used as ornaments. 



2. Calliostoma Swainson. Shell pyramidal, with a flat base, with- 

 out umbilicus; interior pearly: 28 species. 



