434 



NEW YORK STATE MUSEUM 



Observations. This species is one of the few Chazy cephalo- 

 pods which on account of their slender form, the character of their 

 septal necks and siphuncular walls, can be referred to the genus 

 Orthoceras in the restricted scope given to it by Hyatt. 



As similar forms from the Chazy beds suggest themselves O . 

 ( ? ) vagumsp. nov. and Geisonoceras s h u m a r d i . The 

 former has more distant septa and a wider siphuncle but may have 

 been nearly related. G . s h u m a r d i is a straight form, has 

 deeper cameras and a greater rate of growth. 



Orthoceras progressum sp. nov. 



Plate 12, figure 5, 6 



The fragment of a phragmocone on which this species is based 

 permits the elucidation of the following characters : a medium or 



large sized orthoceracoue (fragment has 

 a largest diameter of 34 mm) with cir- 

 cular section and slow rate of growth (as 

 1 to 8). Cameras short (6 mm deep 

 where the couch has a diameter of 34 

 ! mm) ; sutures nearly straight, transversal, 



_ . septa moderatelv concave, the depth equal 



Fig. 13 Orthoceras pro- 1 - 1 1 



gressum sp . nov. Section t0 t j ie leneth of the cameras. 



of^siphuncle. x 1.5 & 



Siphuncle relatively wide (5.5 mm in 

 this specimen) centren in position; the septal funnels short; but 

 slightly bent inward. The siphuncular segments thin, perfectly 

 straight in section [see text fig. 13]. No organic deposits observed. 

 Living chamber and apical part not observed. Surface smooth. 



Position and locality. In the dove -colored limestone of Yalcour 

 island [ Prof. G. H. Hudson coll.]. 



Observations. The specimen in hand preserves in most excellent 

 condition the extremely delicate sculpture of the " Runzelschicht " or 

 second layer of the outer wall, which consists of a system of very 

 fine anastomosing lines passing obliquely across the shell. 



This species differs from () . lentum by its straight conch, 

 straight siphuncular segments and greater width of siphuncle (rela- 

 tively to width of conch and absolutely). 



The centren position of the siphuncle. the great reduction of the 

 siphuncular necks and the corresponding strong development of the 

 secondary siphuncular segments indicate the progressed state of this 

 orthoceracoue when compared with the majority of the other straight 

 shelled ccphalopods of the same formation. 



