BELEM'NITES (Gk. pacp.uov, beionnon, dart, javelin). A genus of dibranehiate cephalo pods of the extinct order Belenmoidea, allied to the modern .quid. That portion of the shell usu ally found is the 'rostrum,' or 'guard,' a solid, cigar-shaped organ, more or less pointed at one end, and pierced at the other extremity by a conical cavity called the 'alveolus.' In perfect specimens there fits into this alveolus a conical chambered shell, the 'phraginocone,' which' seems to be homologous with the similarly chambered shell of the Nautiloidea and Ammonoidea. This phragmocone, which is provided with a siphun cle, has an initial chamber which closely re sembles that of the primitive Ammonoidea, nota bly the genera Baetrites and Mimoeeras, and even more closely the modern dibranchiate genus Spirula, thus indicating the affinities of belem nites. Above the phragmocone, and developed as an anterior extension of its dorsal wall, is the 'pro0straeutn,' a more or less calcified plate that becomes the 'pen' in the modern squid and cuttlefish, and which probably served to protect the vital organs and to give rigidity to the for ward portion of the body. 'flue entire shell was internal.
Some traces of the soft parts of the animal have been found, so that it has been possible to restore the outline of the body and the form of the fins. The general structure seems to have been quite like that of the modern squid, with its long posteriorly pointed body, provided with fin-like marginal expansions of the mantle. There were ten arms, and these were furnished with strong horny hooks that assisted the crea ture to seize its hires. Mandibles, and, most
interesting of all, the hardened contents of the ink-bag have also been, in a few rare eases, pre served. The belemnites are, together with the Ammouioidea, the most characteristic of Meso zoic fossils, and they are found in rocks of Lower Lias (Jurassic) to Upper Cre taceous age, in Europe, North America, and Asia. A single slab of Liassie rock from Whit by, England, now in the geological collection of the museum in Paris, has about 900 specimens on a surface 20 inches square. Some 350 species are known, and they range in form and size from elongated delicate kinds to short, stout varieties.
Belemnites is one of the earliest known fossils, and its history is quite interesting. It has re ceived many names that have expressed various ideas regarding its form, nature, and origin. The shell is supposed to have been known to Pliny. hut the name belenmites was first applied to it by George Agricola in 1546. Previous to that time it had been called 'Unpin-him,' and was supposed to be the urine of a lynx petrified into amber. Popular names were 'devil's-finger' and 'thun der-stone,' and they were used in early times as remedies for nightmare and other maladies. Later naturalists classed them as forms of am ber, stalactites, sea-urchin spines. crocodile and fish teeth, and as chambers in which dwelt small marine animals_ In 1724 Ehrhardt first recog nized their affinity to Nautilus and Spirula. For illustration, see CEPHALOPODA.