BRACmOPODA. 345 
with exceedingly little convexity, appearing in most cases, perfectly fiat. Anterior 
third or half usually uniformly rounded. Front margin occasionally somewhat 
straightened. Sides gently convex to near the beak which, in none of the numerous 
specimens examined, seems ever to have formed an acute termination. Surface with 
only very faint concentric undulations; even these are quite obsolete, when the shell 
is preserved in a shaly or impure limestone matrix." 
Formation and locality.— Hdithav rare near the base of the Hudson River group near Granger and 
Wykolf , Minnesota. It also occurs at Graf, Iowa, and Cincinnati, Ohio. Also in the middle and upper 
portion of the Trenton at Frankfort and Paris, Kentucky. 
Collectors— 'E,. O. Ulrich and C. Schuchert. 
LiNGULA CLATHRATA, tl. Sp. 
PLATE XXIX, FIGS. 42. 
This little Lingula is, in form and convexity of valves, much like L. riciniformis 
Hall, except that it is somewhat wider posteriorly. Like that species, this one also 
shows plainly the Obolella stage of growth. It is, however, much smaller than that 
species, besides differing from it and all associated species of Lingula in-having from 
twenty-two to twenty-eight wavy, imbricating, transverse lines crossing the marks 
of growth and restricted to the external shell layer. These lines begin to appear 
on the medial portion of the valves quite close to the apex, or during early nealogic 
growth. They are closely arranged and gradually become more distant and extend 
across the valve from side to side. Those which are continuous from one margin to 
the other occupy but a small portion of the shell, becoming, disunited medially at 
about one-third the length of the valve from the apex and cease to be developed a 
short distance beyond mid-length or may be continued to near the anterior margin. 
Interior characters not defined beyond a low median septum extending for two- 
thirds of the length of the shell from the apex. 
Length and breadth of an ordinary specimen 4.5 mm. and 2.5 respectively. 
The transverse surface lines appear in a number of other forms occurring in 
older and younger formations. The earliest species with it known to us is Lingidella 
stoneana Whitfield* of the St. Croix formation. The next younger one is the species 
here described followed by Lingula tamiola Hall and Clarkef of the New York Clinton. 
The latter species possesses this feature very strongly developed, obscuring the con- 
centric growth lines, and " are equally visible on the inner side of the shell, a character 
not seen in the other forms. Of precisely the same character is the ornamentation 
in L. zebra Barrande from the Bohemian Etage E.''t L. spathata of the Lower 
Helderberg also has these lines sharply developed and more closely arranged than 
*Uool. Wisconsin, vol. iv, p. 344, pi. xxvii, figs. U. 7; Isfti, tPal. N. Y., vol. viii. pt. i, p. IS; IS*;. JIbiil.. p. IS. 
