72 ZOOLOGY OF THE VOYAGE OF THE SULPHUR. 



299. Trilasmis eburnea, (Plate XXI. fig. 5.) Species unica. 



Inhab. New Guinea. The specimens procured are all attached to the dead 

 or separated spines of an echinus. 



When the number of valves has been deemed of such importance in the 

 formation of the generic groups of this family, no apology seems necessary when 

 introducing another where so few as three complete the shelly covering In pre- 

 vious instances, they have very rarely been observed under five, and from the fre- 

 quency of this number it would appear typical. In the form before us, two 

 flattish, white, oval valves, supported on a peduncle several times shorter than 

 their length, completely cover the animal ; whilst a third, narrow and linear, 

 is situated between their dorsal margins. These offer no other prominent feature, 

 and are otherwise rather conspicuous for their simplicity and uniformity. 



