400 MOLLUSCA: GASTEROPODA. 



ribbon more or less coiled (Natica.) The Whelks (Bue~ 

 cinur/i) and other carnivorous gasteropoda, produce masses 

 or strings of tough capsules, each containing numerous 

 young. 



The Gasteropoda are divided in different ways by dif- 

 ferent writers, according to the value which they attach 

 to the different parts of their structure.* Five groups or 

 Orders are very generally recognized : 



1. PROSOBRASTCHIATA (including Pectinibrancliiata, etc.) are 



those with pectinated gills which are situated near the front of 

 the body, as Strombs, etc. The name coines from the Greek 

 pros, in front, and bragchia, gills. 



2. PuLMONIFEKA or air-breathers ; as Land Snails, etc. The name 



is from the Latin pulmo, a lung, and/m? to bear. 



3. OPISTHOBKAXCHIATA (including Tectibranchiata and Nudi- 



* One of the most, recent classifications is that of Dr. Theodore Gill (see 

 " Arrangement of the Families of the Mottusks prepared for tJie Smithsonian In- 

 stitute, 1871). Dr. Gill divides the Gasteropoda thus : 



Class Gasteropoda or Cephalophora. 



Sub-class DicEca. 



Order 1. Pectinibrancliiata (Strombm, etc.). 

 " 2. Heteropodu (Carinaria, etc.). 

 " 3. Rhipiuoglossa (Ncrita, etc. ). 

 " 4. Docoglossa (Ritella, etc.). 

 41 5. Polyplacophora (Chiton, etc.). 



Sub-class Pulmonifera. 

 Order 6. Pulmonata (Helix, etc.). 



Sub-class Opisthobrnncliiata. 

 Order 7. Tectibranchiata (Bitlla, etc.). 

 " 8. Nudibranclmta (Doris, etc.). 



Sub-class Ptcropoda. 



Order 9. Thecosomata (Hi/alea, etc.) 

 " 10. Gymnosomata (Clio, etc. ). 



Sub-class Prosocephala. 

 Order 11. Solenoconcha; (Dentalium). 



