312 TJie A)nerican Geologist. November, is£9 
to any of the North American Sikirian forms; a Pholidops (Ph. 
trombetana), the beautifully distinct casts of which abound in the 
sandstone. Several new forms of Orthis (O. callactis Dalman, var. 
amazonica, var. nov. ; Dalmanella freitana, and D. smithi) came un- 
der observation. The first form belongs to the normal group of 
Orthis, which reaches its typical development in the age of the 
Niagara and Wenlock periods; the second is very nearly related to 
the Hudson River form O. emacerata, and the third is similar to O. 
testudinaria of the Trenton and Hudson River groups. A Chonetes 
which occurs at the Trombetas is compared by the author with the 
Waldron-form Ch. nova-scotica. For a most interesting little brachio- 
pod the term Anabaia has been introduced as denoting a sub-genus 
of Anoplotheca. Subsequently, in the Palaeontology of New York, 
vol. viii, Part ii, the sub-genus has been raised to the rank of a 
genus, and a short description of the same itiserted. While the form 
is peculiar by its abruptly ending plications on the median fold, its 
hinge structure shows it to be the precursor of the Devonian genera 
Leptocoelia and Anoplotheca. Another species of this new genus (A. 
anticostiana) from the middle Silurian of Anticosti. is also described. 
Several new pelecypods were found in the fauna from the Rio 
Trombetas. Among these are two species of Anodontopsis (A. pu- 
tilla and A. austrina), the former of which may be compared with 
Hall's Nucula obliqua from the Hudson River group, while possibly 
both belong to Barrande's genus Sluzka from the uppermost lower 
Silurian of Bohemia. Two new Tellinomyas, viz. T. pulchella and T. 
subrecta, are described. T. pulchella has a remote similarity with T. 
curta Hall of the Clinton group. Clidophorus brasilianus, sp. n., ap- 
proaches nearest to C. planulatus Conrad, of the Trenton limestone. 
Of gastropods only a Bucaniella, very much like but considerably 
larger than Conrad's B. trilobata of the Medina and Clinton faunas, 
and two imperfect casts of a Murchisonia were found. 
The Pteropoda are represented by a Tentaculites (T. trombetensis, 
sp. n.), which finds a near ally in the T. distans of the Clinton group 
described by professor Hall as a Cornulites), and a small-sized Con- 
ularia (C. amazonica), which presents a very close resemblance to 
Hall's C. niagarensis, especially to the small variety described by Dr. 
Foerste from the Clinton group of Ohio. 
The presence of cephalopods in the fauna of the sandstone is indi- 
cated by fragments of an Orthoceras and of a Cyrtoceras; and the 
crustaceans are represented by Primitia minuta Eichwald (Leperditia 
[Isochilina] cylindrica Hall, from the Utica and Hudson River 
groups) and Bollia lata Vanuxem, var. brasiliensis, which shows some 
minor dififerences from the common Bollia lata of the Clinton fauna. 
The analysis of this fauna verified the opinion expressed by Derby 
as to the Silurian age of the sandstone of' the River Trombetas. It 
is the oldest fauna yet described from Brazil, and the graptolites re- 
cently described from this region by Katzer do not indicate greater 
age. The most interesting feature of this fauna is that it shows a 
