70 J. D. MACDONALD ON METAMORPHOSIS OF GASTEROPODA. 



I next observed a stout little shell, mucli resembling a Macgillivrayia in form, but 

 having the spire more minute and sharply marked, and the whorls beset with epidermic 

 spines, disposed in close spiral lines. The microscopic examination of the animal gave 

 unmistakeable proof of its being a Ranella, the lingual dentition agreeing, at least gene- 

 rically, with my figures and specimens. The rachidian plates of Ranella are boomerang- 

 shaped, with the convexity in front, bearing a recurved angular process divided into sharp 

 denticles. There is often also a small tooth on the posterior border of each arm, near its 

 outer extremity, Tlie uncini of the first series are sickle-shaped and serrulated, with a 

 tooth on the inner side of the base, and those of the second and third claw-shaped, 

 simple. 



On examining the operculum, which in Ranella is so very remarkable, exhibiting three 

 successive stages of growth, I found that it was quite of the same character, only that it had 

 but yet attained the second stage. Einally, on comparing the whole operculum, and the 

 little shell, respectively, with the nucleus of the operculum, and the apex of the shell of 

 an advilt Ranella obtained on the reefs, I could detect no points of difference, even with 

 magnifying powers ; the conclusion, therefore, is irresistible, that the one is but the young 

 state of the other. 



The young of Triton was also determined by the same mode of analysis, and I have 

 been able to confirm my former conviction, that Clieletropis belonged to the Muricidce, 

 and that certain other pelagic shells, which I also figured and described, were referrible to 

 the NaticidcB and Strombidce respectively. 



Of Macgillivrayia I obtained a new species, closely resembling that named 31. ecliinata 

 by Mr. A. Adams, only that the spines, which are disposed in a single row on the dorsum 

 of the whorls, were perfectly straight and not " recurved ;" and the later additions made 

 to the outer lip extended as a thin lamina over the whorls towards the apex of the shell, — 

 a condition which I have also discovered in the young of Triton, and which affords one 

 amongst many reasons for i)lacing Dolinm and Malea (to which the several species of 

 Ilacgillivrayia appear to belong) with Triton and Ranella in one natural family, culling 

 them from amongst the very numerous and heterogeneous genera of the two families, 

 Strombidce and JBiiccinidce, in wliich they are at present to be found. AU these animals 

 have a protractile proboscis with a septiserial lingual ribbon, partaking of the characters 

 of that of Rcmella, as above described. A pair of lateral oral plates, in general composed 

 of indurated rhomboidal cells, is also invariably present ; and if these particulars cannot 

 be affirmed of a genus selected for this family from some fancied resemblance of its shell- 

 characters, nothing is more certain than that some other natural family will be minus a 

 member. 



I obtained once more the little Gasteropod which I was unfortunate enough to name 

 Jasonilla, it having previously, according to Mr. Adams, received no less than three titles, 

 viz. Brownia (D'Orb.), Echinospira (Krohn), and Calcarella (Souleyet), though the ana- 

 tomy of the animal remained unknown. I am now fully satisfied that the true shell is 

 developed within the outer cartilaginous case which rejoices in the above synonyms, and 

 that it is merely the young state of Lamellaria (a Gasteropod with a concealed spiral shell), 

 of which we obtained a living specimen at the Cato lleef. 



