Miscellaneous. 297 



2nd. That the coat is uniformly spread over the whole surface of 

 the shell ; in all parts of the shell it is only formed of a single series 

 of spicula placed side by side parallel to each other and perpendi- 

 cular to the surface of the shell, and that the spicula gradually in- 

 crease in length, and consequently the coat in thickness, as the shell 

 increases in size and thickness. 



3rd. That this velvet-like coat bears no resemblance to any spe- 

 cimens of sponge that have come under my examination ; the spicula 

 are not interwoven or felted together, but are placed parallel to each 

 other in a most uniform manner ; and the coat always presents a 

 uniform and even surface, and never shows any inclination to form 

 prominences or branches on the surface, which is the habit of all the 

 sponges I have seen which envelope and are parasitic on shells or 

 other marine animals. 



4th. Our previous knowledge of the ceconomy of Mollusca has 

 prepared us to believe that they can secrete siliceous bodies and 

 form appendages on the surface of the periostraca separate from the 

 body of the shell. Mr. Hancock has shown that the teeth on the 

 tongue of various Gasteropodous Mollusca are siliceous, and he has 

 shown that the surface of the foot and of various parts of the mantle 

 of different acephalous and gasteropodous Mollusca is studded with 

 siliceous granules, by which these animals are enabled to rasp away 

 the surface of different marine bodies. 



Well-preserved specimens ofLucina pennsylvanica have each of the 

 concentric ridges which ornament the surface of the shell fringed 

 with a membranaceous or semicartilaginous expansion, which is 

 edged with a series of most beautiful, regular, thick, convex, pearl- 

 like pieces of shell, and the concentric ridges which cross the whorls 

 of the outer surface of the horny operculum of Liopa (Delphinula, sp. 

 Lam.) are fringed with beautiful regular subglobular pieces of shell. 



I may further observe, that the outer surface of the periostraca of 

 many shells, both univalve and bivalve, is often covered with short 

 crowded hair-like processes forming a velvety outer coat, as is easily 

 seen in various species of Pectunculus, Buccinum, Triton, &c. 



I am therefore inclined to believe that in these Trigones every layer 

 or line of periostraca which is added to the edge of the one before 

 deposited is furnished with a series of erect siliceous spicula, which, 

 in conjunction with those previously deposited, form the velvet-like 

 coat of the periostraca found in that genus of bivalve shells. 



Though I am not willing to adopt the views of my friends Drs. 

 Fleming and Johnson, yet I think that the discovery of the velvet- 

 like coat of the Trigona being formed of siliceous spicula, is a most 

 interesting addition to our knowledge of the ceconomy of Mollusca. 



THE TORTOISE-SHELL OF CELEBES*. 



Amongst the more valuable of the commodities which the enter- 

 prising and industrious Bugis annually bring to us from Celebes and 



* Translated from the ' Verhandelingen van het Bataviaash Genootschap 

 van Kunsten en Weienschapperi,' vol. xvii. p. i. 



Ann. ft Mag. N. Hist. Ser. 2. Vol. iv. 20 



