16 LECTURES ON MOLLUSCA. 



whence they "btore the name lyncurium. The writers of the middle 

 ages called them " ghosts' candles," "devil's fingers," " night mare's 

 arrows," &c. The more learned supposed they might be petrified 

 amber, fossil dates, stalactites, or spines of sea urchins. It was not 

 till the beginning of the present century that their true nature was 

 understood. The grooved Belemnitdla mucronata, which is charac- 

 teristic of the chalk and Upper Green Sand, is found on both sides of 

 the Atlantic. 



Although the Belemnite itself has not been found preserved, its 

 next door neighbor, the Belemnoteutliis, has been discovered at Chip- 

 penham, (England,) with its shell, muscular mantle, fins, ink-bag, 

 funnel, eyes, arms, and horny hooks, all complete, as if thrown by 

 the tide upon our present shore. The hooks are formidable weapons, 

 from twenty to forty pairs appearing on each arm. In this creature 

 the guard is very thin. In Conotenthis, an active swimmer of the 

 Neocomian age, we have a very long pen terminating in a phragmo- 

 cone shaped like a paper funnel; forming an exact transition from the 

 Squids to the Belemnites. 



Family SPIRULIM:. 



The shells of Spirula are as common in tropical seas now, as were 

 the Belemnites in those of the middle ages. Their resemblance to the 

 pearly nautilus and other allied chambered shells, and especially to 

 the fossil Gyroceras, or Crioceras, is very striking. Here is a loosely- 

 coiled spiral shell, regularly divided by concave sejJta, like the Nauti- 

 lus, each one pierced by a tubular siphuncle. But the resemblance is 

 superficial only. The last chamber of the nautilus tribe is always 

 large, and contains the animal, which is fastened to it by powerful 

 muscles. Whereas the last septm of the Spirula is almost close to 

 the margin, indicating that it is an internal shell, enveloped in the 

 mantle of the cuttle-fish like the bone of the Sepia. Although the 

 shell always forms part of the fancy collections from the Bahama 

 Islands, and it is scattered by thousands on the shores of New Zealand, 

 a perfect specimen of the animal has not yet been seen. It is, how- 

 ever, formed on the usual decapodous type ; only the fins and arm-cups 

 are very small. The ink-bag lies against the last chamber of the shell. 

 Beautiful as the Spirula is, it is still more so when the outer coat on 

 one side has been removed, by allowing it to float on dilute muriatic 

 acid, so as to display the siphuncled septa. 



Among recent shells, the Spirula stands by itself; but it is connected 

 with the Belemnites and Squids by fossil forms. In Spirulirostra, 

 from the Miocene of Turin, we have a very loose spiral siphunculated 

 shell immersed in a kind of cuttle bone of irregular shape. In Bellop- 

 tera, a fossil of the Nummulite age, the chambered part- is nearly 

 straight, and surrounded by a "bone" formed by two inverted cones 

 with winged processes between. In Belemnosis, a unique fossil of the 

 London Clay, the bone is not winged. In Helicerus, a fossil described 

 by Professor Dana from the slate rocks of Cape Horn, there is a guard, 

 as in the Belemnites, inclosing a chambered shell somewhat spiral at 

 the nucleus. 



