CHITONID^. 339 



SO imitate the Iceland fishermen, who pretend that the "sea 

 bugs " are an effectual remedy against this malady, and also 

 that they quench thirst. Perchance the deglutition of these 

 strange bolusus might by anticipating the evil rob a sea-passage 

 of its horrors. — Jeffreys, British. Conchology. 



Section I. — Ghitones Regulares. 

 Head- and tail-plates similarl}^ articulated. 



A. Leptoidea. 

 Insertion-plates obsolete or, if present, unslit. 



{Extinct Forms.) 



The secondary and tertiary Chitons all belong to recent genera. 

 The following are all palaeozoic. A large number of the fossils 

 described as Chitons (for instance Sulcochiton Grayi^ Hj^ckholt) 

 are not mollusks ; many of them being valves of Balani or frag- 

 ments of isopod crustaceans. 



HELMiNTHOCHiTON, Salter. Shell elongated, regular ; mucro 

 regular, subcentral ; terminal valves not sinuated ; apophyses 

 unknown. Distr. — 2sp. Silurian,Devonian; Europe. G.Grijfithii^ 

 Salter dxxxv, 58). 



GRYPHOCHITON (Gray), Carpenter. Shell elongated ; lateral 

 laminae none, suturals small, separated by a wide, simple sinus ; 

 mucro incurved like the beak of a Grjphxa. ; posteriorly and 

 anteriorly strongly sinuated. Distr. — 4 sp. Carboniferous; 

 Belgium. C. prisons, Miinster (Ixxxv, *70). 



CHONECHITON, Carpenter. Shell Leptoidal, the central valves 

 like Grryphochiton, the last with posterior mucro, infundibuli- 

 form. Distr. — Carboniferous ; Belgium. C. viseticola, Ryck. 

 (Ixxxv, 59). 



PRiscocHiTON, Billings. Leptochiton, with posterior lamina 

 excavated within. Distr. — L. Silurian ; Canada. C. Canadensis, 

 Billings (Ixxxv, 64-66). 



PTEROCHiTON, Carpenter. Shell elongated, Leptoidal ; valves 

 laterally excavated, posteriorly acuminated ;. last valve regular, 

 the mucro Ischnoidal ; anterior valve (usually ?) sinuated ; apo- 

 physes large, sinus wide. Distr. — 6 sp. Devon. ; Ireland, 

 Belgium, etc. G. eburonicus, Ryck. (Ixxxv, 6T). 



LORiciTEs, Carp. Related to Lorica, from which it differs in 

 the absence of laminae of insertion. Fossil. Type, C. concen- 

 tricus, Koninck. 



PROBOL^UM, Carpenter. Shell Leptoidal, elongated, largely 

 projecting ; central valve with the central area extending in front 

 of the jugum ; anterior valve sinuate, posterior valve (?). Among 

 recent forms this comes nearest to Katherina, but the difference 

 is still extremely great. Distr. — Devonian of Vilmar. P. cor- 

 rugatum, Sandb. 



