Dr. J. E. Gray on the Structure of Humphreyia. 17 



shell, including its tubular prolongation, is exposed, giving it 

 the appearance of a specimen of Vermetus or Serpula ; and, 

 like the Vermeti, the tube is covered with a distinct thin peri- 

 ostraca. 



When the shell is more carefully examined, it is clear that it 

 has been formed by a conchifer ; for, like Aspergillum, the two 

 valves of the young animal are to be seen forming a kind of 

 umbo at the dorsal part of the base of the tubular projection. 



But instead of the animal, as in Aspergillum, living free in 

 the tube until it has attained its full size, and then fixing the 

 shell in the substance of the tube itself, and closing its base, 

 the animal of Aspergillum Strangei evidently attaches itself, 

 shortly after it is hatched, by its ventral surface, to some fixed 

 body ; and then, as it requires room for its increased size, 

 produces the hinder part of its shell into a projecting tube. 

 For it is evident that the valves themselves are expanded 

 below and on the sides, and are produced behind into the 

 subquadrangular tube with a circular aperture; while, in the 

 true Aspergilla, the valves are imbedded in the substance of 

 the tube, and are to be seen, in all the species of the genus, of 

 their full size, and with a well-defined edge on the inside of 

 the tube; in some kinds only the umbones, and in others a 

 larger part of the valves, being left exposed on the outer surface 

 of the tube. 



The valves of the newly -hatched free animal of Aspergillum 

 Strangei are very soon united together, by shelly matter deposited 

 on their inner surface, into a single shield-like shelly plate, 

 which is extended on the sides ; and the gap between the valves 

 in front and below is filled up with a shelly deposit, which, with 

 the united valves, forms a slipper-like bag attached by its ventral 

 or lower side to the surface of some shell or rock ; so that the 

 shell has changed from a free, regular-shaped bivalve shell to a 

 sessile, attached, slipper-like case. The shell is then gradually 

 extended behind into a tube, as the animal requires a larger 

 cavity for its protection, the periods of its enlargement being 

 marked by transverse concentric impressed grooves. 



The part of the tube in front of the valves is irregularly pro- 

 minent, and scattered with shelly tubes, showing that the ani- 

 mal, like Aspergillum, is furnished with thread-like tentacles on 

 the front of its mantle, which are emitted through these tubes ; 

 and there is also a series of holes, often placed in pairs, and 

 sometimes produced into flat processes, on the edge of the ven- 

 tral part of the tube, just above the part which is attached to 

 marine bodies, doubtless for the protrusion of similar tentacles. 

 The cavity of the shell is quite simple, without any indication 

 of the shape of the two valves which are seen externally, or of 



Ann. $ Mag. N. Hist. Ser. 3. Vol. ii. 2 



