Occasional Papers of the Museum of Zoology 59 



give the shell much the appearance of some species of Thy- 

 sanophora. In the bleached specimen the epidermis is gone 

 and the growth-lines appear quite regularly parallel, but, under 

 a lens, the larger excrescences can be made out as compara- 

 tively slight, local developments of the growth-wrinkles. My 

 specimens appear to be slightly more flattened above the sub- 

 angulate periphery than in those figured by Fischer and Crosse 

 (1902). The largest specimen measures: altitude, 8.8 mm.; 

 greater diameter, 200 (17.7 mm.); lesser diameter, 170 (14.9 

 mm.). 



In the specimen that Avas almost adult the remains of the 

 dried animal w^ere found, and the jaw and radula were obtained. 

 The jaw^ (fig. 10) is broadly arcuate, has a central superior 

 angulation, and bears 11 low, broad, striate ribs. The cutting 

 edge has a transparent border, which is apparently much thin- 

 ner than the basal portion. 



The radular formula (fig. 8) is : 



I 7 26 3 



C — ;L — ;M h — ; or 36-1-36. 



3 3 3-5 4 



The central tooth is comparatively broader than in A. coac- 

 filiata, and is definitely tricuspid. The ectocone and entocone 

 are borne rather near the tip of the mesocone, but are on the 

 same level or slightly above it. The first 7 laterals are also 

 definitely tricuspid. Beyond this, the teeth become more elon- 

 gate, and the entocone is often bifid. Beyond the twenty-eighth 

 tooth, the ectocone also is often double. The outermost teeth 

 seen are short, very variable, and multicuspid. There may 

 be a denticle or so beyond the outermost tooth detected, as 

 the outer portion of the basal membrane was lost, due to 

 trouble in mounting. Nevertheless, the vestigial character of 



