156 MANUAL OF THE MOLLUSCA. 



Animal with, a broad head, destitute of tentacles ; eyes sessile on promi- 

 nent rounded lobes ; gill ? single. The siphonarise are found between .tide- 

 marks, like limpets ; Mr. Gray places them with the pulmonifera, between 

 auriculidre and cyclostoniidse. 



Distr., 30 sp. Cape, India, Philippines, Australia, New Zealand, Pacific, 

 Gallapagos, Peru, Cape Horn (Cuming). 



Fossil, 3 sp. Miocene . 



FAMILY XIV., DENTALIAD^. Tooth-shells. 

 DENTALIUM, L. 



Type, D. elephantinum. PL XL, fig. 27. 



Shell tubular, symmetrical, curved, open at each end, attenuated pos- 

 teriorly ; surface smooth or longitudinally striated ; aperture circular, not 

 constricted.* 



Animal attached to its shell near the posterior, anal orifice ; head rudi- 

 dimentary, eyes 0, tentacles ; oral orifice fringed ; foot pointed, conical, 

 with symmetrical side- lobes, and an attenuated base, in which is a hollovv 

 communicating with the stomach. Branchiae 2, symmetrical, posterior to th( 

 heart ; blood red (Clarke) ; sexes united ? Lingual ribbon wide, ovate ; 

 rachis 1 -toothed ; uncini single, flanked by single unarmed plates. 



The tooth-shells are animal-feeders, devouring foramiiiifera and minute 

 bivalves ; they are found on sand, or mud, in which they often bury them- 

 selves. The British sp. range from 10 100 fms. (Forbes.) 



Distr., 30 sp. W. Indies, Norway, Brit., Medit., India. 



Fossil, 70 sp. Devonian. Europe, Chile. 



FAMILY XV., CHITONID^E. 



CHITON, L. 



Etym., chiton, a coat of mail. 



Ex., C. squamosus, spinosus, fascicularis, fasciatus. PI. XL, figs, 

 Shell composed of 8 transverse imbricating plates, lodged in a coriaceou * 

 mantle, which forms an expanded margin round the body. The first sevei . 

 plates have posterior apices; the eighth has its apex nearly in front. The 

 six middle plates are each divided by lines of sculpturing into a dorsal and 

 two lateral areas. All are inserted into the mantle of the animal by processe 

 (apophyses) from their front margins. The posterior plate is considered ho 

 mologous with the limpet-shell, by Mr. Gray ; the other plates appear lib : 

 portions of its anterior slope, successively detached. The border of the mantle 

 is either bare, or covered with minute plates, hairs, or spines. 



D. gadus of Montagu is an annelide, belonging to the genus ditrupa. 





