'brachiopoda. 467 
Zygosplra niodesta.] 
la the nepionic stage of this form, in specimens about 1 mm. in length,'the shell 
ie depressed-convex without striations and plications, the beak of the ventral valve 
being erect and perforated by a large triangular delthyrium. This stage agrees 
essentially with the same age in species of lihynchonella* and lihynchotrema incequi- 
valvis. In some individuals of Z. recurvirostra the plications begin to develop along 
the anterior margin much earlier than in others. During the succeeding stages of 
growth the valves attain greater gibbosity, the delthyrium of the ventral valve 
becomes partially closed by the deltidial plates, the beak incurves over that of the 
dorsal valve and the striae become larger until a certain size is reached, after which 
new ones are introduced maintaining their equality. 
Z. uphami appears to be a descendant of Z. recurvirostra. It differs in having 
attained a larger growth and greater convexity. The striae, however, do not increase 
in size, but numerous new ones are added, so that Z. uphami appears more finely 
striated. 
Formation and locality. — This species occurs throughout the* Trenton shales, but is very abundant 
near the base of the Galena shales in association with PltQlidops trentonensis, var. minor, Orthis pectinella, 
var. sweeneyi, and Rhynchotrema incequivalvis at Minneapolis, St. Paul, Cannon Falls and Fountain, Min- 
nesota. Also common in the Galena south of Cannon Falls and Kenyon, Minnesota, and at Oshkosh, 
Wisconsin. Near the top of the Trenton in association with Orthis borealis Billings, at Lexington, Dan- 
ville and Frankfort, Kentucky. Martinsburgh, Lowville and Middleville, New York; Ottawa, Canada. 
Collectors.— C. L. Herrick, W. H. Scofleld and the writers. 
Mus. Reg. Nos. 437, 439, 735, 767, 4069, 5477, 5511, 8220-8223. 
Zygospira modesta (Say) Hall. 
PLATE XXXIV, FIGS. 42-44. 
1847. Atrypa modesta Hall. Palaeontology of New York, vol. i, p. 141, pi. xv, flg. 15. 
1859. Genus ? modesta Hall. Twelfth Annual Eeport, N. Y. State Cabinet of Natural History, 
I). 66. "Related to LeptocceZta." 
1860. Atrypa modesta Hall. Ibidem, Thirteenth Report, p. 69, 
1862. Zygospira modesta Hall. Ibidem, Fifteenth Report, p. 154. 
1863. Rhynchonella ? modesta Billings. Geology of Canada, p. 211, flg. 211. 
1867. Zygospira modesta Hall. Twentieth Report, N. Y. StateCab. of Nat. Hist., p. 267, flgs. 1, 2. 
1873. Zygospira modesta Meek. Palaeontology of Ohio, vol. i, p. 125, pi. xi, flg. 4. 
1875. Zygospira modesta Millek. Cincinnati Quarterly Journal of Science, vol. ii, p. 58. 
Original description,: " Suborbicular or plano-convex, with the beak extended; 
width a little greater than the length; cardinal line distinctly marked and somewhat 
extended ; dorsal [ventral] valve convex, with an elevated ridge along the center, 
occupied by four plaits which are stronger than the others; beak promineuj;, incurved 
and perforated, the perforation [pedicle opening] extending below the beak and 
occupying a portion of the area; ventral [dorsal] valve depressed-convex, broadly 
oval or nearly circular, with a broad but ill defined sinus along the middle, the 
central plication stronger than the others, with a smaller one on each side; each 
*The Devolopinuut of some Silurian Bracliiopocla. By Beeeher ami Clarlvo. Mem. N. V. State Mus., vol, i, no. I. ISft). 
