Rathbun.] 34 [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-fifths 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 Moecurii there is a variety resembling much in ap- 

 pearance R. Hors/orfli Hall. It has finer plications and a greater 

 proportionate breadth than the common Brazilian Ibrm, and the fold 

 bears five plications. In a fine micaceous sandstone at the falls of 

 Teuapixima, on the Rio Maecurii, were found small specimens of this 

 species, resembling more the Erere than the Ma3curu variety. The 

 shell of this form is very thin and delicate. At the same locality 

 were encountered Spirifera Pedroana and Tentacutites Eldregianus, 

 but no other fossils. 



Erere. (Morgan Ex., 1871.) Rios Maecuru and Curua. (Geol. 

 Comm., 1876.) 

 Amphigenia elongata Hall. 



Pentamerus 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. Kensxelceria elongata Hall, Palaeont. of N. Y., Iii, p. 453; Twelfth 

 Report on the State Cabinet, N. Y., p. 37, 1859. Siricl-i'a'ulia elon- 

 gata BilVmgs, Canadian Jour. no. xxxiii, p. 268, 1861; Geology of 

 Canada, p. 371, 1863. Amphigenia elongata Hall, Palaeont. of N. Y., 

 IV, p. 383, pi. Lix, 1867. 



This large species of Brachiopod is very abundant in the sand- 

 stone beds of the Rios Maecuru and Curua. 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 



