340 
PALEONTOLOGY OF NEW YORK. 
selves externally. Productus is normally covered with spines on one or both 
valves, but there are some species which jjossess none. The cardinal area, 
deltidium and teeth, which are retained in Chonetes, Productella, Strophalo- 
siA and Aulosteges, become wholly obliterated in the direct line of productoid 
development. In all these forms the “ reniform impressions” retained on the 
inner surface of the brachial valve, are evidence of fleshy brachia possessing a 
similar curvature to those of the Strophomenid^. 
This group of genera has long been designated by the family name Productidje 
introduced by Gray in 1840, though, in correlating the various divisions of 
IVaagen’s proposed group, Aphaneropegmata, there would be excellent reason 
for considering the chonetids and productids components of a subfamily infe¬ 
rior in value to the STROPnoMEmDjE and equivalent to the divisions OrthothetincB, 
IVaagen. 1884, and Rafinesquinina,, Schuchert {cmendatus), 1893.'^ 
Pvcturning to the point of departure, we shall find that in the genus Orthis, 
which in its broadest significance is tantamount to the family Orthid^, Wood¬ 
ward, 1852, since the elimination of several heterogenous branches, the delti¬ 
dium was resorbed at an early stage of growth, leaving the delthyrium a wide, 
uncovered aperture during all the later stages of existence. The pedicle in 
this group of shells was undoubtedly large and vigorously functional through¬ 
out all mature conditions, as it is of very rare occurrence that any secretions of 
calcareous matter are found in the apex of the delthyrium, such as are frequently 
observed in mature and senile conditions of Spirifer. The sharp delimitation of 
the pcdicle-cavity containing all the muscular scars of the pedicle-valve, which 
occurs in the earlier forms (those of Orthis in its restricted meaning, such as 
0. calladis, 0. costalis, etc.) is maintained in all the numerous subdivisions of 
the genus, with the exception of Rhipidomella in which there is a great expan¬ 
sion of the muscular scars, similar to that in the Stropuomenid^ and to which 
reference has just been made. Otherwise the sessile condition of the spondy- 
lium is not modified throughout the entire history of this group. 
The elevation of the spondylioid plate, or the base of the pedicle-cavity, into 
a true spondylium, is a phenomenon of equally early age to the two conditions 
^ Amei'ican Geologist, vol. xi, p. 153. 
