78 



SHELL GALLEEY. 



Fig. 4. 



hinge, the dead valves of dried shells easily fall apart. The peduncle, 

 which is sometimes over six inches in length, passes between the 

 pointed posterior borders of the valves. Dr. 

 Frangois gives a very interesting account of 

 the habits of Lingulaanatina yvhich he found 

 living in the sand at Noumea, New Hebrides. 

 The sole evidence of the animal's existence 

 is the presence, on the surface of the sand 

 or mud, of a small, three-lobed slit (Fig. 4, 

 upper figure). The tube (Fig. 4) in which 

 the Lingula lives is about four inches deep, 

 flat in the upper half, rounded below. The 

 walls of the upper flat portion simply con- 

 sist of the sand with a surface coating of 

 mucous secretion ; but in the lower end the 

 sand grains are agglutinated so as to form a 

 distinct tube. 



The edges of the mantle-folds are pro- 

 vided with setse (bristles), which form three 

 funnels protruding through the three lobes 

 of the slit-like mouth of the sand-tube ; 

 currents enter by the lateral funnels and 

 leave by the central. 



On the least alarm the animal is rapidly 

 withdrawn as far as the centre of the tube 

 (see the dotted line of the shell in the figure), 

 the surface slit and upper part of the tube 

 being obliterated. Each of the arms forms 

 a spiral with several coils (Fig. 5). The 

 Lingulidm are of exceptional interest, in that 

 they furnish a very remarkable example of 

 " persistence of type." 



Shells of Lingula occur in the earliest 

 Paleeozoic strata, and so closely resemble 

 those of the present day, that often no 

 difference can be observed either in the shape 

 of the valves or in the muscular impressions 

 on their inner surface (Fig. 6). 



Lingula occurs in the Indo-Pacific, Aus- 

 tralia, China, Japan, and the Pacific Islands. 

 Glottidia, a smaller form, with two small 



Lingula anatina in tubes 

 in the sand ; upper figure 

 shows trilobed opening on 

 surface of sand. Dotted 

 line in lower figure indi- 

 cates position in retrac- 

 tion. (After Fran9ois.) 



