Vol I, 



Grabau — Ordovician Fossils from North China 



(I) 45 



Fig. 2. 



Fig. 3. 



either flat or slightly arched inwards with depressed sides. In its general form and 



character the final endosheath suggests the conotheca of the Belemnite which is 



prolonged forward into the delicate blade-like 



proostracum, or the similar blade of the o- 



dern cuttle-fish. This blade-like prolongation 



slopes ventrad until it apparently joins the 



wall of the siphuncle on the ventral side. On 



the dorsal side, the blade may have been 



covered by the shell of the siphuncle, but of 



this there is no positive evidence. Indeed 



the sections negative it, although it is of 



course conceivable that the shell was broken 



away before burial. 



The endocone is triple in character. 

 In the genotype the main part has a sub- 

 quadrangular to sub-crescentric cross-section, 

 but appears to taper into a more or less flat- 

 tened conical alveolus towards the apex. On 

 the ventral side, where the wall of the endo- 

 cone is prolonged into the blade, the inner 



surface is gently convex i. e. arched upward (Tlieannulatlons of the surface are not represented.) 



(dorsally) with the sides sharply depres- 

 sed (see text fig. 7). The upper surface of 

 this cavity is flat or nearly so, except for 

 the median portion, which is prolonged 

 dorsally into a broad notch or emargina- 

 tion, on either side of which lie the 

 dorso-lateral alveoli. The outer wall of 

 these is rounded, but the inner wall con- 

 sists of two limbs, approximately at right 

 angles to each other, one, the dorso- 

 ventral limb, separating it from the 

 median prolongation of the main cavity, 

 the other being horizontal and dividing 

 the lateral and main alveolar cavities (see 

 text figs. 4 and 7). The position of this 



Fig. 2. Chihliocerns Kiithani. Dorsal view of a mo- 

 del of the siphuncle of this species with the compound 

 endocone in place. Two thirds natural size. 



Fig. .3. Childioci'ras naihaiii. Side view of the same. 



Fig. 4. 



Fig. 5. 



Fig. 4. Chihliocerns natliani. Dorsal view of a model of 

 the final endosheath, which forms the compound endocone of 

 the siphuncle of this species. Two thirds natural size. 



Fig. 5. Chihlioceras nalhani. Side view of the model of 

 the endocone shown in fig. 4. Two thirds natural size. 



