340 PALEONTOLOGY OF NEW YORK. 



pelves externally. Prodcctos is normally covered with spines on one or both 

 valves, but there are some species which possess none. The cardinal area, 

 deltidium and teeth, which are retained in Chonetes, Productella, Strophalo- 

 siA and AoLOSTEGES, 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 Pnonvcrw^ 

 introduced by Gray in 1840, though, in correlating the various divisions of 

 Waagen'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 Strophouekid^ and equivalent to the divisions Orthothetiruz, 

 Waagen, 1884, and Rafinesquinince, Schuchert (emendatus), 1893.* 



Returning to the point of departure, we shall find that in the genus Orthis, 

 which in its broadest significance is tantamount to the family Ort/iid^, Wood- 

 ward, 1852, since the elimination of several heterogenous branches, the delti- 

 dium was resorbed at an early stage of growth, leaving the delthyriura 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 pedicle-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 

 O. callacUs, 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 Strophouenid^ 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 



* Ameiican Geologist, vol. xi, p. 1S3. 



