1861.] M. O. A. L. MORCh's REVIEW OF THE VERMETID^. 147 



of neighbouring tubes which stop their development. Saxicava and 

 other genera of burrowing Bivalves afford sufficient examples of the 

 generic and specific value of this character. 



The colours are exceedingly variable in one and the same species, 

 and often offer a good guide to determine the genus in the absence 

 of the operculum. The young shells are generally of a brownish 

 colour ; the adults vary sometimes from brown or black to pure 

 white. 



It sometimes appears that the Fermeti, Balani, Ostrece and 

 Anomice not only borrow the sculpture, but even the colours from 

 other shells. It is frequently the case that animals and plants 

 (chiefly sea-weeds) of the most different families and classes living 

 under the same circumstances, are coloured in the same manner. 

 Brewster has shown that the mother-of-pearl colour is received by 

 a cast of melted wax, and consequently is not chemical but purely me- 

 chanical, Uke the different colours of the clouds. A further inquiry 

 will perhaps prove that this fact does not stand quite alone. 



The presence or absence of an operculum is of great generic value; 

 but the tube alone does not seem to afford any character by which 

 the operculated species can be distinguished from the non-opercu- 

 lated. The different manner of interception will perhaps prove of 

 use in this question, but further observations must first be made. 

 The shape of the operculum varies in thickness and convexity ac- 

 cording to age, but this seems not to be of great specific value, 

 although it is indispensable for the generic determination. 



The long bristles of the lid * of the genus Stephopoma afford ex- 

 cellent specific characters. The surface of the lid of Siphonium and 

 some other genera shows nothing particular, even under the lens ; 

 but if softened in water and scratched vrith a knife, some small spiny 

 bodies are obtained, which under the microscope look very like some 

 cylindrical nodulous forms of the Cactus family (see Plate XXV. 

 fig. 16). All the Vermeti seem to be viviparous. The unborn shells, 

 easily found in the dried animals, have the same fixed form and 

 sculpture as shells in general, and are of more consequence for the 

 establishment of species in this family than in any other. 



BuRTiNELLA, Morch. 



Moerchia, Mayer, Journ. de Conch, viii. August, 1860, p. 309, 

 non A. Adams, Ann. and Mag. N. H. April 1860. 

 Vermicularia, Mantell. 

 Solarium, Galeotti. 

 Vermetus, Nyst. 

 Serpula, Phil. 



This genus, which has no interior septa, is perhaps most allied to 

 Siliquarius, which it resembles in the peculiar exterior sculpture, but 

 it differs from it in wanting the branchial slit, like the upper whorls of 



* The only shell before known to have a ciliated operculum is Turritetla ungu- 

 lina, first mentioned by Loven and Forbes and Hanley; but it has been overlooked 

 that the cilia have five small equidistant spines on one side. 



