34 
THE VOYAGE OF H.M.S. CHALLENGER. 
and importance in connection with the phylogenetic relations of the different families of 
Thecosomata. This I shall show in the anatomical portion of this Report. 
Key to the Species. 
A. Shell with simple lip, ..... 
B. Shell with lip exhibiting a tooth towards the suture, 
Peradis reticulata. 
Peradis bispinosa. 
# 1. Peraclis reticulata (d’Orbigny) (PI. I. figs. 7, 8). 
1836. Atlanta reticulata, d’Orbigny, Voyage dans l’Amerique meridionale, t. v. p. 178, 
pi. xii. figs. 32-35, 39, 
1840. Spirialis clathrata, Eydoux et Souleyet, Description sommaire de quelques Pteropodes 
nouveaux ou imparfaitement connus, Revue Zoologique, t. iii. 
p. 138. 
1844. Peracle physoides, Forbes, Report on the Mollusca and Radiata of the iEgean Sea, 
considered as bearing on geology, Rep. Brit. Assoc., 1843, p. 186. 
1865. Spirialis recurvirostra, A. Costa, Di una nuova specie mediterranea di Molluschi 
“ Pteropodi ” del gen. Spirialis, Rendiconto d. real. Acad. d. 
Sci. Napoli, Anno iv. p. 125 (1867); Illustrazione della 
Spirialis recurvirostra, Annuario del Museo Zoologico della R. 
Univ. Napoli, t. iv. p. 56, pi. iv. fig. 12. 
1870. Spirialis physoides, Jeffreys, in Carpenter and Jeffreys, Report on Deep-Sea Researches, 
Proc. Roy. Soc., vol. xix. p. 173. 
1876. Limacina physoides, Jeffreys, New and Peculiar Mollusca of the Eulimidse and other 
families of Gastropoda, as well as of the Pteropoda procured in 
the “ Valorous ” Expedition, Ann. and Mag. Nat. Hist., ser. 4, 
vol. xix. p. 337. 
Characters and Description. — Shell elongated, formed of four bulging whorls, sepa- 
rated by a deep suture, and exhibiting a very slight keel on the side of the spire. 
The latter is somewhat short, obtuse at its apex, owing to the absence of projection 
of its initial portion ; the last turn is very large. The opening is very large, elongated, 
and angled anteriorly. The columella is spiral with a prolonged pointed rostrum, which 
follows in its curvature the spiral of the columella. The surface exhibits a raised 
hexagonal reticulation, the sides of the hexagons bearing a regular row of minute teeth. 
Colour. — Brownish-yellow. 
Dimensions, — Maximum length 4 mm.; diameter 2 ’3 mm. 
Operculum. — Glassy, with about four whorls ; the surface of insertion small. 
Animal. — Corresponding with the generic description. 
Observations. — I. The reticulation of the surface becomes less marked from the apex 
of the spire towards the aperture. On the first whorls it projects markedly, while towards 
the mouth it almost disappears, and the colour of the shell becomes clearer. On the 
