266 



THE SLIT THE TUBED OPERCULATES 



erve the purpose of" admitting water to the branchiae, while 



others are anal. In Trochotoma 

 there are only two holes, united hy 

 a narrow fissure. 



The Tuhecl Land OiKrculates, — A 

 group of the Cyclophoridae, which is 

 restricted to Further India and the 

 great Malay Islands, has developed 

 a remarkable sutured tube on the 

 exterior of the last whorl, near 

 the aperture. A similar tube, but 

 more obscure, exists in Alycaeus. 

 Several stages in the development 

 of this tube may be noticed, begiii- 

 B, Pieurotomaria, c. Schismope, ning with the elcvation of part of 

 D, Polytremaria, E, Haliotis (uot ^]^g peristome Into a simple irregu- 

 drawn to scale). \ -,•, t . , . . , 



lar shelly plate, which is continued, 



first into a short, and then into a long tul:)e, which becomes 

 soldered to the shell ; finally, the tulje becomes free, and the 

 anterior part of the last whorl is disconnected from the spire 

 (Fig. 180 A-D). 



It is singular that the tube does not appear to be of any use 

 to the animal, since its internal extremity, in the complete form, 



E D 



Fig. 179. — The slit in A, Bellerophon, 



Fig. ISO. — Development of the tube in the tul)ed operculates : A, Pterocycvs rxqyestris 

 Bens. ; B, Opisthoporus hirostris Pir. ; C, Sjjiracidum travancoricum Bedd. ; D, 

 Rhiostoma Housei Plr. 



is closed, and does not communicate with the interior of the 

 whorl. It may be presumed, however, that in origin the tube 

 served as a means of conveying air to the animal when the 

 operculum was closed. The holes in the peristome of Fupina, 

 Catauhis, and Anostoma (Fig. 154) may be compared. 



