742 NEW YORK STATE MUSEUM 



apical extremity theciferous, three to four tubular thecae, directed away from 

 the apex, inclined at an angle of about 20°, four times as long as wide, in 

 contact about one half of their length, outer margin slightly concave, apertural 

 margin normal to the axis of the theca. Sicula not observed. 



Position and localities. Common in graptolite beds 

 1 and 2 of the Deep kill zone with Tetragraptus ; at Point 

 Levis in the same horizon. 



Remarks. The term, monodon, is a misnomer, for the 

 long apical tooth is flanked by two lateral teeth. In Dr 

 ^ ,„. ^ . Grurley's specimen one of these has, as the figure indicates, 



Fig. lOoDawsonia J r ' o ' 



Prom the "Beekmantow^ been brokcu away, thus leading to the misconception. 



shales at Point Levis, _ ^ 



Guriey) ^^'^ (Copy from 'pj^g rcmaiiiiug lateral mucro has apparently been taken by 

 the author of the species for a denticle, representing a 

 theca. Our material, however, demonstrates [fig.23] that the thecae are to 

 be found on the narrow, tapering lower extremity. 



There extends on the film a broad and low, but well defined ridge 

 longitudinally from the theciferous tapering end to near the blunt, upper 

 end. This appears to be enveloped by a gradually widening conical mantle, 

 proceeding or suspended from the rounded upper end and terminating below 

 the middle, its lower margin being produced into the lateral mucros. The 

 whole has the appearance of a single theciferous branch, extending the 

 whole length of the organism and protruding at the lower (distal) end, the 

 upper (proximal) portion of which is, (on all sides ?) surrounded by a conical 

 bag. As the rhabdosome does not show any indications of having been 

 attached in any way, it would here, as in the preceding species, su£;gest itself 

 that the bag rejDresents some form of hydrostatic apparatus. 



A difficulty to the uuderstanding of this form is presented by the 

 direction of the thecae aw^ay from the distal point or apex. This direction of 

 growth appears identical with that in the Axonophora, but in the latter the 

 sicula is always to be found at the farthest ends of the rhabdosomes, from 

 which the thecae then grow in a backward direction toward the center 

 of the colony. In the present species, hoAvevei', nothing that would be 

 comparable to a sicula is to be found at the supposed farthest theciferous end. 



