190 



ANCEIM. 



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 



Jr. 



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 



