CEICK : PROOSTRACUJI OF BELEMNITE. 119 



sepiostaire^ the present specimen supports the view ^ that the phragmo- 

 cone corresponds to the inner portion of the sepiostairc ; that the 

 epicuticula of the phragmocone, with its dorsal expansion, corresponds 

 to the middle layer, or to the gladkis of other forms ; and that the 

 rostrum or guard corresponds to the outer portion of the sepiostaire. 

 Whether the dorsal expansion of the epicuticula of the phragmocone 

 alone forms the proostracum, or whether its dorsal surface was wholly 

 or in part covered by a forward continuation of the guard, this speci- 

 men offers no evidence whatever ; hut it seems to show that the wall 

 of the phragmocone did not enter into the formation of the proostracum. 



EXPLANATION OF PLATE IX. 



Eio. I. Ventral aspect of proostracum displayed on slab marked A. 

 ,, 2. Coimterpart of Fit;'. 1 as seen on slab marked B. 

 ,, 3. Lower portion of Fig. 1, somewhat enlarged. 

 ,, 4. Restoration of proostracum, the lower portion being the epicuticula of, and 



containing, the phragmocone : the guard is omitted. 

 ,, 5. Median section of the lower part of Fig. 4, showing the relation of the 



phragmocone to the proostracum. 



a. anterior border of phragmocone ; g. guard ; mr. midrib of proostracum ; 

 ph. wall of phragmocone ; pr. proostracum ; s. last septum of phrag- 

 mocone ; si. siphuncle. 



' See Dr. E. Riefstahl, " Die Sepienschale und ihre Bezielmngen zu den Belem- 

 niten " : Paheontographica, vol. xxxii (1886), pp. 201-14, pis. xxvii, xxviii. See 

 also A. Appellof, " Die Schalen von Stpia, Spirilla, und NaittiUis'''' : Kongl. Sveuska 

 Yetenskaps-Akademiens Ilandlingar, Bd. xxv, No. 7, 1893. 



