CHAPTER VL 
PARTULA GIBBA Férussac—GUAM. 
GENERAL CONSIDERATIONS. 
In the Manual of Conchology, Pilsbry unites the several species of Partula which 
inhabit the Mariana Islands into a new section of the genus called MARIANELLA, 
and of this section Partula gibba is designated as the type; by virtue of this represent- 
ative position, its nature and variations are specially significant. It is the most 
abundant of the four species found in Guam and occurs also in the islands of 
Saipan and Tinian. Its intrinsic diversification has been carried to a much greater 
degree than in the case of radiolata, both in the variety of the distinctive color- 
forms and in the geographical localization of such components as well. In all 
respects, therefore, the present species is the most varied and the most valuable 
for the study of the problems under investigation. 
Partula gibba was first collected by the naturalists of the Freycinet expedition 
of 1819, and the original examples were described by Férussac in 1821 at the same 
time that P. fragilis was established. There is no question that the type material 
came from Guam and that it was collected by the botanist Gaudichaud-Beaupré. 
The zoologists Quoy and Gaimard were also members of this expedition, which 
explored Tinian and Rota but not Saipan; they returned in 1828 as members of the 
Astrolabe expedition under d’Urville, and were well acquainted with gibba, as 
indicated by their comments cited below. The species is recorded by von Prowa- 
zek? as an inhabitant of Saipan and Tinian. Whether or not Rota is also the home 
of gibba remains to be determined. 
The taxonomic record of gibba begins with the original description by Férussac 
(Joc. cit.), here given in translation substantially as it appears in Pilsbry’s Manual: 
Shell conic-ovate, perforate, rather solid, striatulate, pellucid, engraved longitudinally 
with equal lines, white or flesh-colored, the spire acute, rose-red, the suture milk-white; 
epidermis thin, rufescent. Whorls 4%, the last swollen, gibbous, larger than the rest. 
Aperture long-ovate, subquadrangular; peristome reflexed, broadly dilated, white. 
Var. ruddy-black. Habitat, the Mariana Islands. 
In the general account by Freycinet,’ figures are given of two adult shells and 
of one very immature individual; the first belongs to a typical color-class hereinafter 
distinguished as mitella, while the second is recognizable as a member of a sharply 
contrasted color-class, castanea. The young shell is not colored. 
Quoy and Gaimard describe the animal under the name of Helix gibba and 
repeat the orignal diagnosis of Férussac.*| They distinguish and figure a variety 
which is undoubtedly the separate species P. radiolata; their statements have been 
fully discussed in connection with that species and do not require repetition. In 
commenting on gibba these authors say: “This mollusc is very common at Guam, 
one of the Mariana Islands, although it does not inhabit all parts of the island. 
1 Férussac, Tableaux systematiques des animaux mollusques, etc., p. 66, 1821. 
2S. von Prowazek, Die deutsche Marianen, 1913. 
4 Freycinet, L. de. Voyage autour du monde de l’Uranie et la Physicienne, zoologie, p. 485, plate 68, figs. 15, 16, 17, 1824. 
4 Quoy and Gaimard, Voyage de l'Astrolabe, vol. 2, p. 113, plate 9, figs. 18 to 20, 1833. 
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