J3tctumar of "Ummatclf Mature. 307 



at the base, the second joint being generally 

 clothed with hairs directed upwards at its 

 extremity. The caterpillars are cylindrical, 

 and either spinose or furnished with several 

 pairs of long fleshy appendages ; and the 

 chrysalides are often ornamented with bril- 

 liant golden spots. The species belonging 

 to this family are entirely exotic, of a mode- 

 rately large size, and of very varied colours. 

 In some of the species the wings are quite 

 denuded of scales and in many they are but 

 slightly covered. One of the species, Euplcea 

 (JMiiKifs) Jiamata, is said to be so abundant 

 in New Holland, that it occasionally dark- 

 ens the air from the clouds of them. By 

 many authors this and the allied genera are 

 placed in the separate family Danaidce. We 

 must refer our readers to Mr. Doubleday's 

 elaborate letter-press to his work on the 

 Diurnal Lepidoptera, so beautifully illus- 

 trated by Mr. Hewitson. 



HELICTIS. A genus of carnivorous 

 Quadrupeds allied to the Skunks, of which 

 there are at least two species, one found in 

 China, where it was discovered by Mr. Reeves, 

 the other in Nepal, whence it was sent by 

 Mr. Hodgson. 



HELIORNIS. A genus of Birds found in 



South America. [See FINFOOT.] 



HELIX : HELICID.E. The general name 

 of a large and most extensively diffused class 

 of Molluscous animals with a shelly covering. 

 It is equally adapted to the hottest and the 

 coldest climates, the most cultivated and the 

 most barren situations. In the Cuvierian 

 system this is the type of a family of ter- 

 restrial and air-breathing Gasteropods. The 

 common Garden Snail of this country, and 

 the Edible Snail of France and Italy, are 

 well-known examples of this family ; but in 

 tropical climates more striking ones are to 

 be found. The work of Dr. Pfeiffer is the 

 latest and the most elaborate on this group. 

 In the works of Wood, Sowerby, Reeve and 

 others, a great number of species are figured. 

 An inspection of the cases containing them 

 in the British Museum will show how varied 

 their forms are, and how beautifully coloured 

 are many of the species. There are some 

 brought from the Philippine Islands by Mr. 

 Cuming, which when wetted lose their co- 

 lour, but regain it when dry. This is owing 

 to the nature of the epidermis. [See Sx AIL.] 



HELMET-SHELL. (Cassis.} A family 

 of shells, of which there are several species, 

 mostly found on tropical shores, but some 



are also met with in the Mediterranean. 

 They are inhabited by molluscous animals, 

 some of which grow to a very large size, re- 

 quiring of course a corresponding magnitude 

 of shell. They live at some distance from 



the shore, on the sand, into which they oc- 

 casionally burrow, so as to hide themselves. 

 The back of the Helmet-shell is convex, and 

 the under part flat : the mouth is long and 

 narrow : the lip is strongly serrated, and 

 rises into a high thick border or ledge on the 

 back ; and the pillar is generally strongly 

 toothed, and beset with small asperities. 

 The shells of the Cassis rufa and other spe- 

 cies are beautifully sculptured by Italian 

 artists in imitation of antique cameos, the 

 different layers of colouring matter resem- 

 bling the onyx and other precious stones 

 formerly used for this purpose. 



Upon this subject some interesting par- 

 ticulars were detailed by Mr. J. E. Gray, at 

 a meeting of the Society of Arts, held April 

 21. 1847. He observed that numerous at- 

 tempts have been made to substitute various 

 materials, such as porcelain and glass, for 

 the ancient cameos ; but their great in- 

 feriority has caused them to be neglected. 

 The best and now most used substitutes are 

 shells; several kinds of which afford the 

 necessary difference of colour, and at the 

 same time are soft enough to be worked 

 with ease and hard enough to resist wear. 

 The shells used are those of the flesh-eating 

 univalves, which are peculiar as being formed 

 of three layers of calcareous matters, each 

 layer being a perpendicular lamina placed 

 side by side. The cameo cutter selects those 

 shells which have the three layers composed 

 of different colours, as they afford him the 

 means of relieving his work ; but the kinds 

 now employed, and which experience has 

 taught him are best for his purpose, are the 

 Bull's Mouth (Cassis rufa) from the Indian 

 Seas, the Black Helmet (Cassis Madagas- 

 cariensis), a West Indian shell, the Horned 

 Helmet (Cassis cornuta\from Madagascar, 

 and the Queen Conch (Strombus gigas), a na- 

 tive of the West Indies. The two first are 

 the best shells. After detailing the pecu- 

 liarities of these shells, Mr. Gray proceeded 

 to {jive an account of the progress of the art, 

 which was confined to Rome for upwards of 

 forty years, and to Italy until the last twenty 

 years, at which period an Italian commenced 

 the making of them in Paris ; and now 

 about three hundred persons are employed 

 in this branch of trade in that city. The 

 number of shells used annually thirty years 

 ago was about three hundred, the whole of 

 which were sent from England ; the value 

 of each shell in Rome being 30s. To show 

 the increase of this trade, the number of 

 shells used in France last year was nearly as 

 follows : 



Bull's Mouth - 80,000 Is. 8d. 6,400 



Black Helmet - 8,000 5s. 1,800 



Horned Helmet 500 2s. 6d. 60 



Queen Conch - 1,200 Is. 2^d. 700 



100,500 shells. Value 8$GO 



The average value of the large cameos made 

 in Paris is about six francs each, giving a 

 sterling value of 32,0007., and the value of the 

 small cameos is about 8,0007., giving a total 

 value of the cameos produced in Paris for 



