BRACHIOPODA. 295 



Genus PLECTAMBONITES, Pander. 1830. 



PLATE XV, FIGS. '26-29, 32-36; and PLATE XVa, FIGS. :«,:». 



1828. LeptWiM, Dai.man. Kongl. Vetenskajis .\ca(l. Hamlliiii;-., p. lO'.l. pi. i. tig. 4 (not pp. 10(5-108). 

 1830. Plectamhonites. Pander. Beitr. zur Geognosie des russisoheii Reiches, p. 00. jil. iii, tig-.w. 8, 16; 



pi. xxviii, tig. 19 (genei'ic tigmes) ; pi. xix, tig. I. 

 LeptcBna, of Davidson, 1853, 1871 ; Zittel, 1880; CEhi.ert, 1887, Jind authoi-s generally. 

 1840. Stnyphonuna, Conkad. Ann. Rept. Geological Survey of N. Y., p. 211. 



1842. St rophoviena, Kmmons. Geology of N. Y. ; Rejit. Second Di.stric.t, p. 394, tig. 10."). 



1843. Strophomena, Hall. Geology of N. Y. ; Rept. Fourth District, p. 104, tig. 4 ; p. 72, tig. 1. 

 1847. Leptcena, Hall. Palaeontology N. Y., vol. i, p. 110, pi. xxxi B, fig. 2; p 387, pi. Ixxix, tig. 3. 



1852. Leptwna, Hall. Palaeontology of N. Y., vol. ii, p. 59, pi. xxi, fig. 1 ; p. 256, pi. liii, fig. 5. 

 1856. LepUena, Billings. Canadian Nat. and Geol., vol. i, p. 41, tig. 2; p. 138, pi. ii, tig.s. 14, 15. 

 1863. LepUHna, Billings. Geology of Canada, p. 163, fig. 139. 



1865. Plectamhonites, Shaler. Bull. Mus. Comp. Zoology. No. 4. p. Ii4. 



1873. LeptCBna, Meek. Geol. .Survey of Ohio, vol. i, p. 70, pi. v, fig. 3. 



1874. Leptwna, Jame.";. Cincinnati Quarterly Journal of Science, vol. i, p. 151. 



1875. LeptcBiia, Miller. Cincinnati Quarterly Journal of Science, vol. ii. p. 57. 



1879. Leptwna, Ulrich. Journal Cincinnati Soc. Nat. Hist., vol. i, p. 15, pi. vii, fig. 12. 



1853. Leptwna, Hall. Ann. Rept. N. Y. State Geologist for 1882, pi. xv (46), figs. 25-29, 34-36. 

 1885. Leptwna, Foerste. Bull. Denison University, vol. i, p. 79. pi. xiii. fig. 5. 



1887. Plectamhonites, Shaler. Mem. Kentucky Geol. .Surv., V(}1. i, pt. 2. 



Diagnosis. Shells usually small, normally concavo-convex. Surface cov- 

 ered with very fine striae, often alternating in size. Hinge-line making the 

 greatest width of the shell, the extremities often subauriculate. Cardinal area 

 narrow in both valves, sometimes obscurely crenulated on the margins. Pedicle- 

 valve with a moderately broad delthyrium which is partially closed by a convex 

 plate, but mostly occupied by the cardinal process of the opposite valve. Apical 

 foramen sometimes retained. Teeth prominent and supported by thickened 

 plates, which are continued in broad outward curves for more than half the 

 length of the valve, returning and uniting in the umbonal cavity, thus limiting 

 two linguiform muscular scars, enclosing a more or less clearly defined adductor 

 impression. 



In the brachial valve, the dental sockets are deep, and often appear to tran- 

 sect the cardinal area. The cardinal process is simple and erect but by its 

 coalescence with the short prominent crural plates, the posterior face appears 

 trilobate. The crural plates end abruptly as in Orthothetes ; becoming thick- 

 ened at about the middle of their length, giving origin to two low ridges or 

 septa, which at first approach each other, and thence continue forward with a 



