27G POLYPI.ACOJ'HORA uK LoRlJ HOWR ANO XOKFOLK 1SLAXD8, 



Remui'ks. — This veiy striking shell is frequently found on the 

 hUick polished basalt shingle, and its brilliant white colour is in 

 marked contrast with its surroundings. It resembles the Aus- 

 ti'alian A. costatus in the strongly ribbed anterior and median 

 \ alves, but differs from that species in the size and shape of the 

 pustules; is broader and more elevated. 



5. ACANTHOCHITES APPROXIMANS, n.Sp. 



(Plate xii., figs. 5, 5r<, bh, be, bd, 5^, 5/!) 



Shell elongated, elevated, carinated. Colour pale yellow, 

 flamed with dark to pale olive-brown. 



Anterior valve densely sculptured with elongated pustules 

 arranged in radiating rows. 



Posterior valve similarly sculptured, but pustules more sepa- 

 rated and less regularly arranged; dorsal area similar to median 

 valves; mucro sub-prominent, in front of the middle. 



Median valves : latero-pleural areas not differentiated, sculp- 

 tured with irregular radiating rows of flattened pustules; dorsal 

 areas broadly wedge-shaped, convex, longitudinally deeply striate, 

 the sti'ite crossed by growth-lines. 



Girdle olivaceous, densely clothed with rather long spicules; 

 sutural tufts large, silvery. 



Interior white; siiuis broad, shallow, minutely crenulate. 

 Anterior valve having f), and median valves 1-1 slits. Pijsterior 

 valve with two slits separated by a posterior sinus. 



Length 11 mm., bieadth 4-5 mm. 



Station. — On the uiuler side of stones, or in the ijiterstices of 

 coral rock, in pools at low tide. 



Habitat. — Lord Howe and Noi'folk (tyiie-locality) Islands. 



Remarks. — This .shell is raie in both localities. It closely 

 resembles the Australian species, ^1. yranostriahis Pilsbry, par- 

 ticularly in colour- pattern, l)ut the grains on the Australian 

 species are fewer and more prominent, and the head-vahc of the 

 Island species lacks the incipient ribs of A. gratiostriatus. 



Note. — The figure of the entire shell shows the colour-pattern; 

 the details show the .sculpture. 



