190 



ANCEID^. 



the following cut). Each valve is somewhat of an oval 

 form, the outer edge nearly straight, fitting the somewhat 

 triangular deep impression on the underside of the head : 

 the inner margin of each valve is strongly ciliated, and 



•f f 



along the middle of the disc are three thickened circular 

 calcareous masses (apparently representing the ossified 

 centres of the three joints, of which this portion is pro- 

 bably composed). The somewhat pointed apex of each 

 of these valves is furnished with a minute joint, setose at 

 its tip. These valves are attached near the posterior 

 lateral angles of the head ; they are ordinarily shut 

 together, their inner margins overlapping each other, so 

 as to form an under covering of the head. Within 

 them arises a much smaller and more delicate pair of 

 appendages (possibly homologous with the first pair of 

 gnathopoda) {h but marked / in the above figure), 

 composed of a somewhat square basal piece, with its 



