80 
THE VOYAGE OF H.M.S. CHALLENGER. 
the pallial cavity of the Bulloidea also exhibits a pallial gland (Bulla, Pl. II. fig. 3, d ; 
Scaphander, &c.). This pallial gland of the Bulloidea presents different degrees of 
development ; and in Actseon (PI. I. fig. 6, a), where it is rather large, it is quite identical 
both in form and position with the shield of Limacinidse (PI. I. fig. 5, a). The situation 
of this pallial gland in the Bulloidea close to the gill show T s that it (and consequently also 
the “shield” of the Thecosomata) is nothing else than the hypobranchial gland of the 
Gastropods, which has become asymmetrical in the adult straight Thecosomata in con- 
sequence of an adaptive return to the primitive external symmetry. 1 
The margin of the mantle in the Bulloidea is continued on the right side by a large 
lobe (PI. II. fig, 3,/) which corresponds to the right lobe of the mantle in the Lima- 
cinidse, often called the “ balancer” (PI. I. fig. 1, g). 
The Digestive Tract. 1. Radula. — In the Tectibranchia systematists distinguish 
marginal and lateral teeth. In reality all the teeth of the same transverse row (except 
the central tooth) are similar in form, and pass insensibly from the innermost to the 
outermost by diminishing in size and the gradual loss of the marginal denticulations. 
In the Bulloidea, properly so called, there are only a small number of teeth on either 
side of the central one, for example in Cylichna and in some species of Tornatina 
(Tornatina truncatula= Cylichna truncata 2 ) ; Fischer 3 is wrong in denying a radula to 
the Tornatinidse ; the outer teeth are here very much reduced in size (these are the 
so-called “marginal” teeth), whilst the inner (“lateral”) tooth on either side of the 
median one remain well developed, thus exhibiting a formula which, by degeneration and 
loss of the marginal teeth, comes into agreement with that of the Thecosomata ; 4 this 
formula ( 1-1-1) is in fact exhibited by some of the Bulloidea — Scaphander (Sars), 5 
Ampliisphyra (Loven), 6 Runcina . 7 
The form of the teeth in the Bulloidea is the same as that in the Thecosomata, 
especially the most primitive ones, the Limacinidse. 
2. Salivary Glands. — In Scaphander 8 these have precisely the form and structure of 
those of the Thecosomata, short, ovoid, and with no differentiated duct. 
1 Schiemenz (Ueber die Wasseraufnahme bei Lamellibranchiaten und Gastropoden, Mitth. Zool. Stat. 
Neapel, Bd. v. p. 527) has already recognised the relations between the “ shield ” and the “ mucous ” (hypo- 
branchial) gland of Gastropoda, but he identifies it also with the ink-bag of the Cephalopoda. This homology 
does not hold, for the hypobranchial gland exists in the Cephalopoda, and as there are two gills so there are 
two hypobranchial glands, which have been long known under the name of spleen (“Milz”). Joubin, who has 
studied these organs (Structure et ddveloppement de la branchie de quelques Cephalopodes des Cotes de France, 
Arch. d. Zool. Expdr. ser. 2, t. iii. pp. 115-119), has not recognised their homology for want of comparison. 
2 Formula — 4-1-1-1-4 ; see Forbes and Hanley, History of the British Mollusca and their Shells, pl. vv. fig. 4a. 
3 Manuel de Conchyliologie, p. 555. 
4 In the genus Cylichna, also, the reduction of the number of “marginal” teeth is clearly visible. See Sars, Mollusca 
regionis arcticae Norvegiae, pl. xi. figs. 3 ( Cylichna alba, Brown, 5-1-1-1-5), 4 ( Cylichna cylindracea, Penn., 3—1— 1—1 —3), 
5 (Cylichna propinqua, M. Sars, 2-1-1-1-2). 8 Loc. cit., pl. xi. figs. 13, 14. 
6 Malacozoologi, Ofversigt Jc. Vetensk.-Akad. Forhandl., 1847, pl. iii. ; Forbes and Hanley, loc. cit., pl. UU, fig. 2, c. 
7 Gray, Guide to the Systematic Distribution of the Mollusca in the British Museum, part i. (1857), fig. 114, p. 205. 
8 Vayssiere, Recherches anatomiques sur la famille des Bullides, loc. cit., pl. x. fig. 87. 
