KATHARINA. 41 



lonofitudiDally striated at the apices, scaly at the sides ; lateral areas 

 bi-lirate, the lirre scaly. Posterior valve very small, nearly con- 

 cealed, subquadrate, bi-lirate. Girdle wide, gray, pilose, clothed 

 with whitish down ; tufts 9, white, glassy. 



Length 27, breadth 16 mill. (Eochebr.) 



New Caledonia (Presented to the Paris Mus. by the Colonial 

 Museum.) 



Acanthochites tridacna Rochebr., in Bull. Soc. Philomathique de 

 Paris, 1880-'81,p. 121. 



This is evidently a form allied to A. violaceus and A. costatiis. 

 The seven anterior ribs mentioned evidently include the sutural 

 margins, the number five being constant in this group. 



Genus KATHARINA Gray, 1847. 



Katharina Gray, P. Z. S. 1847, p. 65. Type C. tiuiieatus Wood. 

 — Cpr. in Dall, Proc. U. S. Mus. 1878, p. 312. 



Valves two-thirds covered by the expanded girdle, the exposed 

 portion divided into dorsal and side areas, instead of central and 

 lateral. Insertion plates sharp, extremely long, thrown forward ; 

 that of the head valve with 7-8 slits ; sinus deep, spongy. Tail valve 

 Avith a wide caudal eraargination or sinus, and several slits, often 

 partly obsolete, on each side. Girdle broad, smooth, poreless, 

 leathery. Gills extending the whole length of the foot. 



The poreless girdle, the long (ambient) gills, and the abnormally 

 large number and irregularly placed slits of the head valve, all 

 separate this well-founded genus from related groups. The irre- 

 gularly placed anterior slits it shares with Amicula and Cryjjtochiton. 

 The long gills are also a character of the last-named genus ; but in 

 the multifissate posterior insertion -plate and the naked girdle it 

 resembles Cryptoconchus and Loboj^lax. There is but one species 

 known. 



K. TUNICATA Wood. PI. 1, figS. 1-11. 



Shell oblong, elevated, the valves mainly covered by the black, 

 leathery girdle, a small cordate or flask-shaped area of a dark brown 

 color, remaining exposed. 



The exposed portion is about one-third the entire width of the 

 valve; it is broad behind, and often hollowed out by erosion ; nar- 

 rowing in front like the neck of a flask. The surface when not 

 eroded shows a distinct, smooth and shining dorsal band, the sides 



