6 BRITISH FOSSILS. 



" well on all the laminaj. These last indicate the mode of its pro- 

 " gressive growth, and, consequently, the form which the opening had 

 " during the whole period of its growth. 



" These striae of growth form a series of transverse semicircles, 

 parallel with the sutures of the septa, on the ventral face of the phragmo- 

 cone. There are always many on each alveolar chamber, and they are 

 the closer together the nearer they are to the apex. This arrangement is 

 seen only on the ventral face of the phragmocone ; and when the striae 

 reach the lateral regions they assume an almost hyperbolic curvature 

 to approach the straight lines which pass from the apex of the cone 

 and run, between the side and the back, as far as the aperture. I 

 shall call these lines the asymptotes, and the lateral regions where the 

 striae have a hyperbolic curvature, hyperbolic area (regions hyper- 

 boliques) ; the region between the asymptotes I shall term the dorsal 

 area (region dorsale). The transverse strias sometimes unite in groups 

 into a single line, when they take the hyperbolic curvature and ascend 

 towards the asymptote. The width of the dorsal area, that of the hyper- 

 bolic area?, the quantity and the curvature of the strias of these different 

 areae, vary according to the species ; but this variation is very slight. 

 The width of the dorsal area is usually about one-fourth of the circum- 

 ference, and that of each of the hyperbolic areas an eighth. 



" The stria? of the dorsal area are less numerous than those of the 

 rest of the test, and are usually less pronounced than the latter, being 

 sometimes imperceptible ; they form ogive arcs, the apex of which is 

 turned towards the aperture of the shell. Often, one sees a slightly 

 raised straight line, which sets out from the apex of the cone and in- 

 tersects the summits of all the ogives ; at other times a groove traverses 

 the region ; and occasionally the ogives are not visible. 



" It would appear from these facts that the ventral edge of the 

 aperture of the phragmocone is parallel to the sutures of the septa, 

 and that, on the sides, it curves round almost at a right angle to form 

 an elongated lobe, which terminates in an ogive arch on the dorsal 

 side." 



The existence of these conothecal strife has been noted by all 

 observers, and Voltz's clear description of their distribution and 

 direction has been largely confirmed. I shall have to point out, how- 

 ever, that one species of Belemnite, at any rate, exhibits a different 

 pattern. 



The view taken by Agassiz and Voltz of the nature of the Liassic 

 pens, formerly referred to Loligo and Onychoteuthis, met with strong 

 opposition in an essay by Prof. Quenstedt, entitled " Loligo Bollensis 

 1st kein Belemiten Organ," and published in Leonhard and Bronn'-s 

 Jahrbuch for 1839. 



Prof. Quenstedt points out, with great justice, firstly, that the mark- 

 ings on the pens are quite different in character from those on the 

 phragmocones of any known Belemnites ; and, secondly, that the 

 posterior ends of the pens are complete, and certainly were not united 

 with any such structure as a Belemnite, while it is impossible to 

 imagine that the latter should have been attached to the anterior ends 

 of the pens. 



In 1 840, however, M. Voltz, in his " Observations sur les Belopeltis 

 ou lames dorsales des Belemnites,"* brings forward new arguments in 

 favour of Agassiz' opinion. 



Memoires de la Societe d'Histoire Naturelle de Strasbourg June 1840. 



