Rathbun.] ‘4 [May 15, 
down abruptly. The fold begins a little posterior to the middle and 
increases gradually in size forward, its width at the front equalling 
two-fitths to one-half the width of the valve. 
There are from fourteen to eighteen plications on each valve, of 
which from three to four occupy the fold? and two to three the sinus. 
Size of a large specimen; length 18 mm., breadth 23 mm.; but this 
is above the average. Although. the sinus and fold are both generally 
well defined at the sides, yet on many of the smaller specimens they 
are only slightly marked, and in a few examples there are either two 
or five plications on the fold, and two or four in the sinus. These 
are rounded or subangular on top, and the depressions separating 
them are subequal in size, or slightly narrower or broader. 
From the Rio Mecurti there is a variety resembling much in ap- 
pearance f. Horsfordi Hall. It has finer plications and a greater 
proportionate breadth than the common Brazilian form, and the fold 
bears five plications. In a fine micaceous sandstone at. the falls of 
Teuapixima, on the Rio Mecuru, were found small specimens of this 
species, resembling more the Ereré than the Mecuru variety. The 
shell of this form is very thin and delicate. At the same locality 
were encountered Spirifera Pedroana and Tentaculites Eldregianus, 
but no other fossils. 3 
Ereré. (Morgan Ex., 1871.) Rios Mecurt and Curud. (Geol. 
Comm., 1876.) 
Amphigenia elongata Hall. , 
Peniamerus elongatus Vanuxem and Hall, Reports Third and 
Fourth Geol. Dists. N.Y., pp. 132 and 34, 1842 and 43. Meganteris 
elongatus Hall, Tenth Report on the State Cabinet, N. Y., p. 123, 
1857. Rensseleria elongata ‘fall, Paleont. of N. Y., 11, p.453; Twelfth 
Report on the State Cabinet, N. Y., p. 37, 1859. Stricklandia elon- 
gata Billings, Canadian Jour. no. xxxul, p. 268, 1861; Geology of 
Canada, p. 371, 1863. Amphigenia elongata Hall, Paleont. of N. Y., 
IV, p. 383, pl. L1x, 1867. 
This large species of Brachiopod is very abundant in the sand- 
stone beds of the Rios Mecuru and Curué. ‘The moulds of the 
shells are generally found in a perfect state of preservation, often 
finely representing the internal characters. In its younger stages of 
-growth the shell is usually short-ovate in outline, afterwards becom- 
ing elongate-oval and often subcylindrical in general shape. A 
‘large specimen has a length of 100 mm.,.and a breadth of 45 mm. 
- The.only-marked. difference. noted. between the, Brazilian form and 
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