338 MOLLUSCS. 



parts of the world. Dried cuttle-fishes are exposed for sale in the bazaars or 

 markets throughout India, and may be seen among the articles of Chinese, 

 Japanese, and Siamese food. The ink of the cuttle-fish was employed as a writing 

 material in very ancient times, its use being mentioned in the works of some of the 

 old Latin writers; the ink-bags of cuttles are still manufactured into sepia by 

 artists' colourmen. Eggs of the common cuttle resemble black pointed grapes, each 

 having a flexible stalk, looking and feeling like indiarubber. They are generally 

 attached to the stems of seaweed. Each capsule contains a single young one. 



Family SPIRULID^:. 



Spirula represents the last of the three divisions into which the living 

 decapods have been divided. The shell of the spirula is abundant on the shores 

 of some tropical countries, but the animal is scarcely ever met with. Only a few 

 specimens have been captured, and most of these are in bad con- 

 dition. The shell is entirely white, pearly within, placed verti- 

 cally within the posterior part of the body, so that the spire 

 corresponds to the ventral side of the animal. It is a loosely 

 coiled structure, resembling a ram's horn, and is divided into a 

 Spirula peroni. number of chambers by fine concave partitions, like the shell of 

 nautilus, each one pierced by a slender tube or siphon near the 

 inner curve of the shell. Three species are known, distinguished by differences 

 in the soft-parts, the shells being similar. 



To the same group as the Spirula belongs the extinct family of 



Belemnitidce, ranging from the Lias to the Chalk, and whose skeletons 



are commonly known as thunderbolts. They possess a tapering chambered shell, 



inserted into the summit of a long spear-like guard. Most of the species belong to 



the typical genus Belemnites. 



FouR-GiLLED GROUP, Order TETRABRANCHIATA. 

 Family NAUTILID^I. 



The nautilus is the sole living representative of this order, and although not 

 so rare as the spirula, the animal of the nautilus is by no means common in 

 collections. It is probably an inhabitant of deepish water, and only likely to be 

 obtained alive by dredging, although a few specimens have been occasionally cap- 

 tured at the surface. The animal is contained within the last compartment (A) of a 

 chambered shell, within which it is completely retractile. It does not resemble any 

 of the dibranchiate cephalopods, having numerous small retractile feelers or tentacles, 

 without any suckers, in place of the eight or ten sucker-bearing arms of that order. 

 The beaks are very solid and calcareous, not entirely horny as in the dibranchiates. 

 The eyes are small, and raised on short stalks ; the funnel is not a complete tube, 

 being formed of two lobes which fold over one another, but are not joined together. 

 To the posterior end of the body is attached a slender fleshy cord, termed the 

 siphuncle (a), which passes through holes in the septa of the shell up the coiled spire. 

 It is enclosed in a horny tube, which is again coated with a calcareous deposit. 



