BRACHIOPODA. 459 



Bhynohotrema uin^liel.l 



RHYNCHOTREMA AINSLIEI N. H. Winchell. 



PLATE XXXIV, FIGS. 1-8. 



1886. Rhynchonella ainsliei N. H. WINCHELL. Fourteenth Annual Report of the Geological and 



Natural History Survey of Minnesota, p. 315, pi. n, flgs. 5, 6. 



This species has the essential characters of R. incequivalvis, therefore a detailed 

 description will not be necessary. It differs from the latter in being usually larger, 

 more transverse, and in having from twenty-eight to thirty-four plications, with six 

 to eight on the fold, and five to seven on the sinus, while R. incequivalvis has from 

 sixteen to twenty-two plications, with four to five on the fold. Compared with 

 Rhynchonella altilis Hall* of the Ohazy group of New York, Rhynchotrema ainsliei 

 is seen to be more transverse, has a more prominent fold and sinus, is less globose, 

 and on the average has a few more plications. 



Formation and locality. Restricted to the lower portion of the Trenton shales, where it is common 

 at Minneapolis, Cannon Falls, Lanesboro, Fountain, Chatfleld and Preston, Minnesota; Decorah and 

 McGregor, Iowa. 



Collectors. C. N. Ainslie, C. L. Herrick, W. H. Scofleld, J. C. Kassube and the writers. 



Mus. Reg. Nos. 324, 326, 734, 4031, 4938, 4974, 5180, 5489, 5492, 5498, 5505, 5512, 5517, 5521, 7917, 

 8204-8207. 



EHYNCHOTREMA IN^EQUIVALVIS Castelnau. 



PLATE XXXIV, PIGS. 9-25. 



1843. Spirifer iniequivalvis CASTELNAU. Essai sur le Systeme Silurien de 1'Ame'rique Septentrionale, 



p. 40, pi. xiv, flg. 8. 

 1817. Atrypa increbescens (partim) HALL. Paleontology of New York, vol. i, pp. 146, 289, pi. xxxm, 



flgs. I3a-13h; ? pi. LXXIX. flg. 6. 

 1856. Rhynchonella increbescens (partim) BILLINGS. Canadian Naturalist and Geologist, vol. i, 



p. 207, flgs. 11-14. 



1863. Rhynchonella increbescens BILLINGS. Geology of Canada, p. 18, flg. 153. 

 1875. Trematospira (9) quadriplicata MILLER. Cincinnati Quarterly Journal of Science, vol. ii, 



p. 60, flgs. 6, 7. 



1889. Rhynchotreta quadriplicata MILLER. North American Geology and Palaeontology, p. 370. 

 1889. Rhynchonella increbescens NETTELROTH. Kentucky Fossil Shells, p. 83, pi. xxxiv, flgs. 26-29. 

 1892. Rhynchonella minnesotensis SARDESON. Bulletin of the Minnesota Academy of Natural 



Sciences, vol. iii, p. 333, pi. iv, flgs. 21-23. 

 Compare Atrypa subtrigonalis HALL. Palaeontology of New York, vol. i, p. 145, pi. xxxm, 



flgs. 12a-12c, 1847. 



The original description of R. increbescens was drawn up from specimens now 

 referred to that species and to R. capax Conrad. That by Castelnau is not accessible 

 at the present time. The following description is based on material derived from 

 Minnesota, Kentucky and New York : Shell small, varying from narrow to broadly 

 subtriangular in outline, smooth in the nepiohic stage, depressed-convex during the 

 nealogic period, and becoming more globose in ephebolic and geratologic growth; 

 posterior lateral margins straight or somewhat convex, rounding rapidly into the 

 sinuous anterior edge. Surface with prominent subangular plications, from sixteen 

 to twenty-two on each valve, with from three to five on the fold, and two to four in 



Pal. N. Y.. vol. i. p.:23. pi. ivbis, fi<ts. Usi-lkl. 



