208 NEW YORK STATE MUSEUM 



probably belongs to the same species; and that at the same time 

 exhibits a well-preserved aperture leaving no doubt of its proper 

 generic reference to Hexameroceras. We will therefore describe it 

 and we take pleasure in naming it after Professor Chadwick who 

 kindly informed us of the opportunity of collecting in the Vernon 

 shale at Pittsford. 



The holotype of the species consists of a living chamber, very 

 much compressed in the axial direction of the cephalopod, but 

 apparently undisturbed in transverse direction. 



The section was oval, with the dorsal and ventral extremities 

 slightly produced and acute, the ventral one more so than the dorsal. 

 The dorso-ventral axis measures 45.5 mm at the widest part; the 

 minor axis 37.5 mm. The length of the much compressed living 

 chamber is about 15 mm. The aperture is 20.5 mm at its widest 

 (dorsal) extremity and about 31 mm long. It consists of six deep 

 brachial sinuses, three on each side, and one median sinus on the ven- 

 tral side. The sinuses decrease in size toward the ventral side, so 

 that at the third pair the aperture is but 11 mm wide. The dorsal 

 brachial sinuses are the deepest; they and the following pair are 

 perpendicular to the axis of the aperture, while the third, sm.allest 

 pair is oblique to the axis. The median sinus is small and continued 

 into the hyponomic slit leading into the hyponomic sinus, which was 

 at the ventral extremity of the shell, but is not fully preserved. 



The siphuncle which is seen on the underside of this specimen, is 

 marginal on the ventral side, and about 7 mm wide. 



Two camerae preserved under the living chamber suggest a low, 

 narrow saddle on the ventral side and a broad, low saddle on the 

 dorsal side. 



A second, smaller specimen (plate 3, figure 9 ) is compressed 

 'aterally and serves to show the shortness of the living chamber, 

 which is 16.5 mm long and 30 mm wide. The camerae are very 

 shallow in depth, about one-twelfth of the greatest width, and the 

 septa seem to have been equally shallow. 



Horizon and locality. Vernon and Pittsford shale at Pittsford 

 N. Y. 



Mixopterus multispinosus (Clarke and Ruedemann) 



Plate I, figures 3-7; plate 2, figures 1-4; plate 3, figures 4-6 



Clarke and Ruedemann (1912, p. 297) have described as S t y - 

 lonurus (Ctenopterus) multispinosus a 

 species of eurypterid from the Pittsford shale, that was based on 

 two walking legs and a sternite. The longer one of the walking 



