"MALACOZOA. GASTEROPODA. NUDIBKANCHIATA. 335 



striulate in its whole length, and having the posterior 

 extremity truncate, with a wide and shallow umhihcus. 

 Pellucidus, pervious to light. 



Shell very similar in form to Bullina truncata, but differing 

 in being destitute of sulci in its upper half, it being glossy and 

 very faintly striulate in its whole length. It is subcylindrical, 

 a little wider anteriorly, where it is rounded ; at the upper end 

 truncate, with the spire sunk, forming a wide and shallow um- 

 bilicus ; the aperture very narrow, but becoming oblong 

 anteriorly, and at its hind part projecting a little in the form 

 of a sinus beyond the extremity of the shell ; the colour 

 hyaline-white. Length two-twelfths, breadth half the length. 



Not very unfrequent adhering to Actiniae from the Bay of 

 Aberdeen. I have also found it on Terebella conchilega 

 there. 



Volvaria pellucida. Brown, Illustr. PI. 38. f. 45, 46. 



5. Bullina producta. Produced Bullina. 



Shell oblongo-cylindrical, thin, transparent, glossy, 

 with faint growth-lines, the apex slightly unibilicate, the 

 aperture extremely narrow, the outer lip forming a 

 narrow sinus projecting considerably beyond the apex. 



Shell more elongated than Bullina pellucida, and having 

 the apex narrowed and rounded, but slightly umbilicate ; the 

 aperture very narrow, the outer lip projecting in the form of 

 a narrow sinus considerably beyond the apex, the anterior 

 end narrower and rounded ; the colour hyaline-white. Length 

 nearly three-twelfths of an inch, breadth nearly half the 

 length. 



Found by me in January, 1843, adhering to Actinia?, from 

 the Bay of Aberdeen. 



Bulla producta. Brown, Illustr. PI. 38. f. 15, 16. 



ORDER VIII. 



GASTEROPODA NUDIBRANCHIATA. P. 69. 



Family II. — Tritonipna. P. 70, 195. 



Genus 2. Sph&rostoma. 



Body oblong, much compressed, flat beneath, convex 

 above in both directions, terminating obtusely behind, 



