156 MANUAL OF THE MOLLUSCA. 



Animal witli a broad head, destitute of tentacles ; eyes sessile ou promi- 

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

 marks, like limpets ; Mr, Gray places tbem with the pubionifera, between 

 auriculidse and cyclostomidfe. 



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

 Gallapagos, Peru, Cape Horn (Cuming). 



Fossil, 3 sp. . ]\Iiocene — . 



FAMILY XIV., Dentaliad^. Tooth-sheUs. 

 Dentalium, L, 



T>/pe, D. elephantinum. PL XL, fig. 27. 



Shell tubular, sjTumetrical, 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 hoUow 

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

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

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



The tooth-sheUs are animal-feeders, devom'ing foraminifera and minute 

 bivalves ; they are found on sand, or mud, in which they often bmy 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., CHIT0XIDJ5. 



Chiton, L. 



Etpii., cliiton, a coat of mail. 



Ex., C. squamosus, spinosus, fascicularis, fasciatus. PI. XL, figs. 28 — 31. 



Shell composed of 8 transverse imbricating plates, lodged in a coriaceous 

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

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

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

 two lateral areas. AH are inserted into the mantle of the animal by processes 

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

 mologous with the limpet-sheU, by Mr. Gray ; the other plates appear like 

 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. 



