L'OO UKI.KMX rm> r. 



'2. A if-mird or rod rum more or less extensively enveloping the 

 M|>i<-:il part of the phragmocone. "The phragmoconc is not a 

 chambered body made to lit into a conical hollow previously 

 formed in the rostrum. :is some have conjcct ured, hut both the- 

 rostrum and cone grew together: the former was formed on the 

 exterior of a secretive surface, and the latter on the interior of 

 .mother secretive surface." ( 1*111 M.I l-s. ) 



The rostrum is composed of calcareous mailer arranged in 

 fibres perpendicularly to ilie planes of the lamime of u'rowth. 

 Professor Owen describes the fibres, in specimens from rhris- 

 t ian Malford. as of a t rihedral prismat ie form, and one 1 \vo-t hous- 

 andth of an inch in diameter. These fibres a re disposed con- 

 centrically around an axis, t he so-called apical line, which extends 

 from the extremity of the phragmoconc to that of the rostrum. 

 Indications of a thin capsule or formative membrane appear in 

 some ]li-li-mnit t 'n investing the guard: in those of the Oxford 

 clay it is represented by a granular incrustation; in some liassic 

 ^pecies it appears indelicate plaits, like ridges or furrows; in 

 some specimens of Hrlt'iiui itclhi nuii-romi/a from the upper chalk 

 of Antrim, it is in the form of a vcrv thin nacreous laver. 



:;. A />ro-0titracn in. or anterior shell, which is a dorsal exten- 

 sion of the ronotlu'ca beyond the end where the iruard disap- 

 pears. The surface of the conotheca is marked by lines of 

 urowth. and. according to Volt/, it may be described in four 

 principal renioiis radiating from the apex ; one dorsal, with loop 

 lino of iiTowth. advancing foi-ward ; two lateral, separated from 

 the dorsal by a continuous straight or nearly straight line, and 

 covereil with very olli|iicly archeil strise in a hyperbolic form. 

 in part nearly parallel to the dorso-lateral boundary line, and in 

 part retlexcd. so ;i> to form lines in retiring curves across the 

 ventral portion nearly parallel to the edges of the sepia. There 

 were at least three kinds of pro-ost racuni in the family B<'l*'in- 



A. In manv /''/ ///////> the extension of tiie mnntlifru seem- 

 to run out in one simple broad plate, as in /I. h<i*l(i(n*. from 

 Solenhofell (% I. 



//. In /li'lnit/i //<.- /'// .os/V/ ////>-. d'( )rbin-n\ . the pro-ost racum is 

 \ery thin, and apparently horny or imperfect ly calcified in the 



