PKOCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 281 



funnel is formed by the laminie 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. 



Chonechiion (Chilon) viselicola Ryckholt, 1. c.,ii. 51, no. 6, pL 3, figs. 10, 11, 1845. Car- 

 boniferous of Vis6, Belgium. 



Priscochiton Billings. 

 Leptochiton: lamina i^ostica apicali, intus excavata. 



Type. 



Priscocliiton canadensis BiUings, Pal. Fos. Canada, 18G5, p. 394, fig. 370, LoTver 

 Silurian. 



Pterochiton Carpenter. 



Lorica elongata, leptoidea ; valv^e lateraliter excavatae, projectse post- 

 ice acuminataB ; val va postica regularis, mucrone ischnoideo ; val va antica 

 (plerumque ?) sinuata; apophyses maximae, sinu lato. Type C. eburonicm 

 Eyckholt. 



Species. 



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



1845. Carboniferous limestone of Vis6, Belgium. 

 Pterochiton legiacus Ryckholt, Bull. 1. c, ji. 52, no. 7, pi. 4, figs. 5, 6. 1845; Chiton 



gemmatus (pars) Koninck, An. Fos. Carb. Belg., p. 323, no. 3, pi. 23, figs. c,d,e 



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

 Pterochiton gemmatus (Koninck) Ryckholt, 1. c, 1845, p. 59, no. 13, pi. 4, figs. 1, 2, 3 



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

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



1859, 111. 4, f. 2 a-c. Carboniferous limestone, County Limerick, Ireland. 

 Pterochiton Sandbergianus (!) Ryckholt, 1. c.,i). 62,1845. Devonian, Vilmar; Schultze. 



(Mus. Comp. Zool.) 

 t? Pterochiton Shiseanns Ryckholt, 1. c, p. ,5, No. 10. (Non C. Sluseanus ejusdem, pi. 



4, figs. 7, 8=^eburonicus.\ Cf. text.) 



Subgenus Loricites Carpenter. 



Eelated to HclminthocMton and to the recent Lorica as above stated. 

 From the latter it diflers in the absence of laminae of insertion. 

 Type CJuton concentricus Koninck, op. cit., 1857. 



Probol^um Carpenter. 



Lorica leptoidea, elongata, maxime projecta; valvis centralibus areas 

 centrales ante areas jugales porrectae; valva antica sinuata, valva post- 

 ica — ? Type G. corrugatnni Sandberger (pars). 



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

 ence is still extremely great. 



* The figures are wrongly named C. Shiseanus on the plate, 

 t Koninck does not escape this error also. 



