WOODWARD : EPHIPPODOjVTA. 



25 



spite of the fact that Epliippodonta is commensual, living as it does in 

 the underground bnrrow of a prawn, it has undergone little or no 

 change of form or structure to better fit itself for that life. The main 

 differences are that its valves have become quite covered by the 

 mantle, and are still more gaping than in Galeomrna, and that it 

 possesses no eye spots on the margin of its mantle. 



Prof. Tate's description of the method of progression of Uphippo- 

 donta is as follows : — 



' ' The animal of both species of Epliippodonta has the creeping 

 habit of Galeomrna ; the valves are flexible and spread out flat when 

 the animal is in motion ; indeed while in life, the valves cannot be 

 brought to a less angle of divergence than about 70°." 



Fischer states of Galeomrna that the animal can attach itself to rocks 

 by means of its byssus, but it also moves with great rapidity and 

 carries its two valves completely spread oat in the form of a disc. ^ 



EXPLANATION OF FIGUEES ON PLATE IL 



The figures were drawn from four specimens, viz. : — two dissections and two series 

 of transverse sections. All the latter were taken in serial order from the posterior to 

 the anterior end of the animal, and the drawings represent the posterior faces of the 

 sections. Figures 3 and 7-18 were drawn with the aid of an Abbe camera lucida. 



FiQ. 1. — Ventral aspect of the animal, x 3. 



,, 2. — Animal with the right mantle lobe and gills removed. 



,, 3. — Tran verse section of the foot and byssal gland, x 20. 



,, 4. ^Foot and gills of the left side seen from below, x 3. 



,, 5. — Animal with the ritrht mantle lobe removed, x 3. 



x3. 



1 Thyreopsis coralliophila (Adams, Proc. Zool. Soc, 1868, p. 14) and Libratula 

 (Pease, Proc. Zool. Soc, 1865, p. 512) both resemble Epliippodonta and Galeomrna 

 in the method of carrying their shells when crawling ; the former presents a further 

 resemblance in the form of the valves. 



