JOO KKLKMMTlh.K. 



2. A t/uard or rostrum more or less extensively enveloping the 

 apical part of the phragmocone. "The phragmocone is not a 

 cliambered body made to fit into a conical hollow previously 

 formed in the rostrum, as some have conjectured, but both the 

 rostrum and cone grew together; the former was formed on tin- 

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

 another secretive surface." (PmLLi is. ) 



The rostrum is composed of calcareous mailer arranged in 

 fibres perpendicularly to the planes of the lamina 1 of growth. 

 Professor Owen describes the fibres, in specimens from Chris- 

 tum .Malford. as of a t rihedral prismalic form, and one two-thous- 

 andth of an inch in diameter. These fibres ;ire disposed con- 

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

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

 Indications of a thin capsule or formative membrane appear in 

 >oine Belemnites investing the guard ; in those of the Oxford 

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

 species it appears in delicate plaits, like ridges or furrows; in 

 some specimens of Bclcm n ih'Hft ninrrnmita from the upper chalk 

 of Antrim, it is in the form of a very thin nacreous layer. 



3.. A pro-ostracum. or anterior shell, which is a dorsal exten- 

 sion of the conothet'U beyond the end where the guard disap- 

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

 growth, and, according to Volt/, ii may be described in four 

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

 lines of growth, advancing forward ; two lateral, separated from 

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

 covered with very obliquely arched st r'ne in a hyperbolic form. 

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

 part retlexcd. so as to form lines in retiring curves across the 

 ventr.-d portion nearly parallel to the edges of the septa. There 

 were at least three kinds of pro-ost racum in the family 

 nitidfr. 



A. hi many Belemnites the extension of the conolhcca seems 



to run out in one simple broad plate, as in /I. //</>/</.///.<. from 

 Solenhofen dig. 4:.:J). 



/!. In llfh'uniiii-x Pwzostantts, d'Orbigny, the pro-ostracum is 

 very thin, and apparently horny or imperfectly calcified in the 



