BRACHIOPODA. 467 
Zygospira modesta.] 
In the nepionie stage of this form, in specimens about | mm. in length, the shell 
is 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 Rhynchonella* and Rhynchotrema ineequi- 
valvis. In some individuals of 7%. 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 striz 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 7%. recurvirostra. It differs in having 
attained a larger growth and greater convexity. The strizw, however, do not increase 
in size, but numerous new ones are added, so that 7. 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 Pholidops trentonensis, var. minor, Orthis pectinella, 
var. sweeney?, and Rhyncholrema inequivalvis 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. LL. Herrick, W. H. Scofield and the writers. 
Mus. Reg. Nos. 487, 489, 735, 767, 4069, 5477, 5511, 8220-8223. 
Zyeosrira MopDESTA (Say) Hall. 
PLATE XXXIV, FIGS. 42—44. 
1847. Atrypa modesta HALL. Paleontology of New York, vol. i, p. 141, pl. xv, fig. 15. 
1859. Genus ? modesta HALL. Twelfth Annual Report, N. Y. State Cabinet of Natural History, 
. p.66. ‘Related to Leptocelia.” 
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, fig. 211. 
1867. Zygospira modesta HALL. Twentieth Report, N. Y. State Cab. of Nat. Hist., p. 267, figs. 1, 2. 
1873. Zygospira modesta MEEK. Paleontology of Ohio, vol. i, p. 125, pl. x1, fig. 4. * 
1875. Zygospira modesta MILLER. 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 prominent, 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 Development of some Silurian Brachiopoda. By Beecher and Clarke. Mem. N. Y. State Mus., vol. i, no. i, 1889. 
