PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 281 



funnel is formed by the lamina3 of insertion ; as these do not exist in the 

 leptoid section, the funnel is seen in the hollowing of tlie back of the 

 valve itself. 



Type. 



Clionechiion (Chilon) visetiwla Ryckbolt, 1. c.,i). 51, no. 6, pL 3, figs. 10, 11, 1845. Car- 

 boniferous of Vis6, Belgium. 



Priscochiton Billings. 

 Leptochiton: lamina postica apicali, iutus excavata. 



Type. 



Priscochiton canadensis Billings, Pal. Fos. Canada, 18G5, p. 394, fig. 370. Loirer 

 Silurian. 



Pterochiton Carpenter. 



Lorica elongatn, leptoidea ; valva? lateraliter excavatse, projectje post- 

 ice acuminatse ; valva postica regularis, mucrone ischnoideo ; val va antica 

 (plerumque ?) sinuata ; apophyses maximie, siuu lato. Type C. ehuronicus 

 Eyckholt. 



Species. 



Pterochiton cburonicus Ryckholt, Bull. 1. c, part ii, p. 53, no. 8; pi. 4, figs. 7, 8,* 



1845. Carboniferous limestone of Vi8<^, Belgium. 

 Pterochiton legiacus Ryckbolt, Bull. 1. c, p. 52, no. 7, pi. 4, figs. 5, G, 1845; Chiton 



(jemmatus (pars) Koninck, An. Fos. Carb. Belg., p. 3'23, no. 3, pi. 23, figs. c,d, e 



(not figs, a, b). Same locality as the preceding. 

 Pterochiton gcnimatus (Koninck) Ryckbolt, 1. c, 1845, p. 59, no. 13, i>1. 4, figs. 1, 2, 3 



(fig. 4, forsitau exclus. ). Same locality as preceding. 

 Pterochiton Thomondiensis Baily, Nat. Hist. Review and Quart. Journ. Sci., July, 



18.")9, pi. 4, f. 2 a-c. Carboniferous limestone, County Limerick, Ireland. 

 Pterochiton Sandberf/ianns (1) Ryckbolt, 1. c.,p. 62,1845. Devonian, Vilmar; Scbultze. 



(Mus. Comj). Zool.) 

 ?? Pterochiton Sluseanus Ryckbolt, 1. c, p. .5, No. 10. (Nou C. Slnseanus ejusdem, pi. 



4, figs. 7, S^^eburonicus.i Cf. text.) 



Subgenus Loricites Carpenter. 



Related to Helminthochiton and to tlie recent Lorica as above stated. 

 From the latter it differs in the absence of lamina? of insertion. 

 Type GMton concentric us Koninck, op. cit., 1857. 



ProbolyEUM Carpenter. 



Lorica leptoidea, elongata, maxime projecta; valvis centralibus arete 

 centrales ante areas jugales porrecta?; valva antica sinuata, valva post- 

 ica — I Type C. corrngatum Sandberger (pars). 



Among recent forms this comes nearest to Kafherina, but the differ- 

 ence is still extremely great. 



* Tbe figures are wrongly named C. Sluseanus on tbe plate, 

 t Koninck does not escape tbis erior also. 



