324 
PALEONTOLOGY OF NEW YORK. 
In Acrotreta, Conotreta, Linnarssonta, Acrothele and Iphidea the pedicle- 
aperture is persistently located at the apex of the pedicle-valve. This group of 
genera is one of very early date, for the most part contemporaneous with Paterina, 
and the existing evidence would indicate that it was not directly ancestral to the 
line of Trematis-Orbiculoidea {DiscmmY). The incipient formation of an inter¬ 
nal foraminal tube is seen in several of these genera (Acrotreta, Acrothele, 
Linnarssonia), and this feature attains its maximum in the true Sipiionotreta 
of the Lower Silurian, where the foramen is still apical and the tube wholly 
internal. Hence Sipiionotreta appears to be a normal termination of this line 
of descent. Sciiizambon, in the comprehensive meaning of the term ascribed 
to it in this work, has the pedicle-passage superficial, and in such shells as 
Schizamhon Jissus, Kutorga, and var. Canadensis, Ami, the condition of this 
passage is perfectly analogous to that of Sipiionotreta, the entire difference 
being in the enclosure of the latter. In Sciiizambon the fibers of the pedicle, 
extending through the foramen near the middle of the pedicle-valve, were 
directed toward the apex of that valve, and along the concave floor of the 
external pedicle-groove. The inner aperture of the pedicle-tube in Siphono- 
treta, corresponds to the “foramen” of Sciiizambon, and the outer aperture’ 
or true foramen of the former to the grooved umbo of the pedicle-valve in the 
latter. Hence in Sciiizambon, thus considered, there is no evidence of a prog¬ 
ress of the external aperture, or true foramen, anteriorly beyond the apex of 
the pedicle-valve. These two genera are but slight departures from the same 
type of structure, but it would appear that this deviation took place during 
primordial times, as the typical Schizambon {S. typicalis, Walcott) is a primordial 
fossil. The newly described genus, Trematobolus, Matthew {T. insignis, Mat¬ 
thew, type), appears to be another primordial representative of this structure, 
with the tubular enclosure of the pedicle more highly developed. Thus all 
these genera, from Acrothele to Sciiizambon and Siphonotreta, possess an 
apical foramen, and the development both of the internal tube and the 
corresponding external groove has been a gradual one. They represent 
termini of slightly divergent series; consequently they may all be safely 
* Canadian Record of Science, January, IS93, pp. 277-279, figs. I a-d. 
