MICROMELO. 391 



10. B. (A.) thalassiarchi AD. in Thes. ii, p. 564, pi. 120, f. 4-6. 

 Aplustrum thalassiarchi SOWB., Conch. Icon., xvi, f. 2. BRAZIER, 

 Proc. Linn. Soc. N. S. Wales, ii, p. 79. 



The near alliance of this species to the Hydatinas is shown in the 

 convex columellar rib which forms the basal spout, as in If. physis, 

 and the pattern (but not color) of the markings, which is exactly as 

 in H. velum. There can be no doubt of the localities given above, 

 as the extreme eastern and western limits are attested by many ex- 

 cellent authorities, and are represented by many specimens before 

 me. 



The shell, when fresh, is covered by a thick brown cuticle, which 

 projects at the lip well beyond the calcareous layer. The black 

 bands are reduced to narrow lines in one lot of about 50 specimens 

 from the Sandwich Is., in the Academy collection ; one of these 

 being represented in fig. 6, but some others have them still narrower 

 and fainter. 



This species has appeared in the books under many names, but 

 by the nature of things none can antedate amplustre of Linnasus' 

 tenth edition of the Systema. 



Genus MICROMELO Pilsbry, 1894. 



Bullina FER. in part (see ant., p. 175). Hydatina Auct. in part. 

 Bullinula GRAY, not Swains. 



Shell oval, rather thin, with exposed nearly flat spire of several 

 whorls and minute, uptilted, subimmersed nucleus. Last whorl large 

 spirally striate-punctate, with a color-pattern of two or three spiral 

 and many wavy longitudinal lines. Aperture pear-shaped, dilated 

 and rounded below; outer lip a little notched at suture; columella 

 concave, with reflexed edge, obscurely folded above. Type M. un- 

 data Brug. 



Animal not completely retractile into the shell; head disc bearing 

 two flat tentacular processes in front, produced behind in two large 

 lobes partly covering the shell. Eyes wanting? Foot large; stom- 

 ach without bony plates ; dentition unknown (pi. 59, fig. 26, M. 

 guamense). 



This genus differs from Hydatina and Aplustrum in the spirally 

 sculptured shell, the animal having two, instead of four tentacular 

 processes on the head disk. I have not followed Fischer in consid- 

 ering B. undata Brug. the type of Bullina Fer. because Ferussac 



