Mr. Robert Garner's Malacological Notes. 365 



Tlie boring or burrowing Lamellibrancliiates are often very 

 aberrant — Pliolas especially in its binge, the valves and mantle 

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

 underlying cells here, with Jin^briw of the mantle lodged in 

 them ; muscular fibres (the anterior adductor) cross from 

 valve to valve at this })art ; and we should suppose that the 

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

 tary eftbrts 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 modifled to meet external condi- 

 tions. Notwithstanding its extreme elongation it is in every 

 respect a true lamcllibranchiate ; 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, spatulce or palettes, 

 guarding the posterior siphons, curiously imbricated and pos- 

 sibly a dismemberment of the valves, analogous to what we 

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

 lojiing 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 the 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 l^lind to the existence of other adaptations to 

 aid, at least, in the perforation of timber. 



The anterior extremity of Afipei-gillum (watering-pot shell) 

 is still more modifled, the valves being curiously fused with 



