74 Lamarck's Genera of Sh<>ll*. 



Shell semicylindrical at the lower part; the upper part attenuated, 

 conical. Fossil — common in limestone, dpi. PI. vi. Fig. 209. 

 2 Species *. (This figure shews the slender process at the apex of 

 the cone, mentioned in the note below ; Fig. 209 is a representa- 

 tion of another, and rarer species, B. mamillata.) 

 2. Orthocera. 



Shell elongated, straight, or slightly curved, subcorneal, striated 



* In the Transactions of the Royal Society of Edinburgh, for 1823, is a very 

 interesting paper by Thomas Allan, Esq., on the " Formation of the Chalk 

 Strata anc! Structure of the Beleninile," to which we refer the reader for much 

 valuable information respecting this curious fossil. Amongst other particulars 

 mentioned by Mr. Allan, and which we wish our limits did not forbid us to 

 quote more in detail, he observes that, " The form of the belemnite is that of 

 a cylinder, terminated at one end with a conical point, famished with a slender 

 process of about a quarter of tin inch in length ; but it is only when the belemnite 

 has been enclosed in flint that this delicate member has been preserved." — 

 " This process proceeds from the apex of the cone, to that of the belemnite." — *' In 

 composition, the belemnites, whether enclosed in lime-stone, flint, clay, or 

 sand-stone, is uniformly formed of crystallized carbonate of lime, striated and 

 radiating to the circumference, from a lime which passes from the apex of the 

 alveolus to that of the fossil." — " A structure quite different from that of other 

 calcareous fossils, which are formed in general of the common rhomboidal 

 carbonate ;" and, " which appears to have been dependent on some internal 

 organization." — " On this account we may, perhaps, he allowed to consider 

 the belemnite as unaltered." Mr. Allan dissected several belemnites imbedded 

 in flint, from Ireland, by means of acid, and found them intersected by minute 

 siliceous cylinders, having exactly the form and appearance of arteries, and 

 connected with each other and with that portion of the cone which remained, 

 by means of smaller fibres representing veins, and affording the most striking 

 resemblance to an injected anatomical preparation." Others, when the 

 calcareous matter was removed, exhibited " small, irregular, globular masses, 

 entangled in " lace-like work," and in others, again, the flint presented an 

 appearance " which may, perhaps, be best compared to the ovarium of some 

 animal." Mr. Allan decides nothing as to the mode by which the siliceous 

 matter may have been introduced into the fossil. Perhaps they may be worm- 

 boles filled lip with the flint; — " the great dissimilarity among the specimens 

 seems to preclude the possibility of attributing their structure to organization, 

 however stron»ly some of them may resemble it." The slender process, 

 however, projecting from the apex of the concamerated cone to that of the 

 belemnite, appears to be uniform ; and, perhaps, the " anatomist may find in 

 the threads by which the rounded masses (in the ovarium-like specimens) are 

 connected, more uniformity than could be attributed to the accidental per- 

 forations of a worm." These various appearances are beautifully represented 

 in two plates annexed to this valuable communication. 



