88 FISTULANA. GASTROCH^ENA. ASPERGILLUM. 



always remains in its hole, with the mouth down and the anus 

 above. The common Teredo^ which is about six inches long, it 

 is said was brought from the torrid zone, but it is widely 

 spread in the seas of France, and infests the dikes of Holland 

 to such an extent that its unperceived ravages have, more than 

 once, been near producing terrible inundations. Vessels have 

 been sunk by the holes bored through their bottoms by these 

 animals. To guard against such accidents, is one among the 

 reasons why ships' bottoms are covered under water by thin 

 sheets of copper. 



19. The FISTULAN^E also live buried in submerged wood or 

 other analogous substances, and also line the interior of their 

 hole with a calcareous mortar which constitutes a tube, com- 

 pletely closed at the large end, having more or less resemblance 

 to a bottle. Like the Teredines, they have externally a small 

 bivalve shell and two plates, which may be regarded as analo- 

 gous to the operculum pieces of the gastcropods. They inhabit 

 the Indian Seas. 



20. The GASTROCH^N^ differ very little from the preceding; 

 their shell, which is unprovided with teeth, is very gaping in 

 front, and their double tube, which can be retracted entirely with- 

 in the shell, is susceptible *of great elongation; they excavate 

 holes in stones or masses of madrepore, and often line these holes 

 with calcareous matter which, on becoming hard, constitutes a 

 tube similar to that formed by the Teredo and Fistulana. 



21. We also place in this division the CLAVIGELLA and 

 ASPERGILLUM, which also construct a calcareous tube; in the 

 first, one of the valves is clasped by the tube, while the other 

 remains free in its interior; and in the last, the tube has, at its 

 closed extremity, a disk perforated by a great many little tube- 

 like holes, an arrangement which has obtained for it the name of 

 " watering-pot shell." 



CLASS OF BRACHZOPOD MOLLUSKS. 



22. These mollusks are very analogous to the common 

 acephalce ; they are also provided with a two-lobed mantle, 



19. What are the characters of the genus Fistulana? (Fistulana, from 

 ihe Latin, fistula, a pipe.) 



20- What are the characters of the genus Gastrocheena ? (Gastrochoma, 

 from the Greek, gaster, helly, and chaind, I gape.) 



21. What are the characters of Clavigella? (Clavigella, from the Latin, 

 clavis, a nail or spike.) How is the genus Aspergillum distinguished ? 

 'vAspergillum, Latin, a watering-pot.) 



2k What are the characters of Brachiopod mollusks ? (Brachiopod, 

 pronounced brak-e-opod, from the Greek, brachion, an arm, and pnus, foot.) 



