Mr. Robert Garner's Malacological Notes. 365 



The boring or burrowing Lamellibrancliiates are often very- 

 aberrant — Pholas especially in its hinge, the valves and mantle 

 being reflected at the umbones, and there being often a row of 

 underlying cells here, with Jimhrice of the mantle lodged in 

 them ; muscular fibres (the anterior adductor) cross from 

 valve to valve at this part ; and we should suppose that the 

 valves are opened somewhat, as well as closed, by the volun- 

 tary efforts of the animal. P. dactylus has several shelly 

 plates covering the reflected part of the mantle, P. candidus 

 only one, but in addition a weak ligament. The valves- have 

 a tendency to become otherwise disintegrated in these boring 

 bivalves ; a calcareous enveloping tube is often formed, and 

 the true valves are much diminished in proportion in Xylo- 

 phaga or Teredo, or even become incorporated with the tube. 

 The body is often strangely elongated, as in the last species. 

 The Teredo or ship-worm is a remarkable example of how 

 much ordinary type may be modified to meet external condi- 

 tions. Notwithstanding its extreme elongation it is in every 

 respect a true lamellibranchiate ; thus the alimentary canal is 

 reflected over the posterior adductor muscle as usual, though 

 to be so it has to ascend within a few lines of the anterior 

 extremity. It has, however, two new parts, spatidce or palettes, 

 guarding the posterior siphons, curiously imbricated and pos- 

 sibly a dismemberment of the valves, analogous to what we 

 shall see in Chiton. In the mature Teredo the shelly enve- 

 loping tube has, in the neighbourhood of the palettes, imper- 

 fect partitions, and it becomes closed at the other extremity. 

 The internal processes or spoons seen in the small valves sup- 

 port and protect the foot and viscera, help to keep together the 

 valves, and give attachment to muscles ; the heart is not per- 

 forated by the rectum, and, with its auricles, is of the shape of 

 the inverted letter j^. Xylophaga has commonly no palettes ; 

 but the foot has a central papilla with an orifice, more deve- 

 loped, however, in Pholas crispata ; and here the curved crys- 

 talline style is inserted, having itself a hard calcareous 

 nucleus ; this must support tlie foot ; and it is possible that 

 there may be a vent here, in the wood-borers, for some soften- 

 ing fluid from the stomach. Though the writer broached the 

 idea that ciliary action, or rather the consequent currents of 

 water, constitute especial agents in the burrowing powers of 

 mollusks &c., and that the fleshy and ciliated foot, aided, it 

 may be, by hard particles, has furthermore much to do with it, 

 yet he was not blind to the existence of other adaptations to 

 aid, at least, in the perforation of timber. 



The anterior extremity of Aspergillum (watering-pot shell) 

 is still more modified, the valves being curiously fused with 



