iL MARINE BIOLOGY OF THE SUDANESE RED SEA. 
Tritonia hombergit (§ Malacologische Untersuchungen,’ in Semper’s Reisen, 
pl. Isai, file: 1). 
The jaws are thin and transparent. No striation or tessellated appearance 
is visible, The edge bears a single row of large and distinct denticles. The 
radula consists of 49 rows with a formula of 30+1+1+1+30 as a maximum, 
but the rows in front are much reduced and the first consists of the median 
tooth only. The median tooth is broad and bears three cusps, but as the 
corners are also raised it might be called five-cusped. The central cusp 
sometimes bears an inconspicuous denticle on either side. The first lateral is 
as usual in the genus. The rest are simple, without denticles, and erect ; 
the inner ones are rather thick ; those nearer the end of the row are much 
thinner and more elegant. The outermost of all is smaller and less well 
formed. 
The cesophagus is short. The first division of the stomach is lined with 
folds, which are stronger in the anterior than in the posterior part ; the second 
division is armed with a belt of about 70 roughly triangular horny plates, 
striated and of different sizes. The intestine is broad and laminated internally. 
The liver is greenish yellow inside, but greyer outside owing to the layer of 
the hermaphrodite gland which covers it. The front part is hollowed out 
and forms two lobes which enclose the greater portion of the stomach. The 
hepatic mass is traversed by large ducts which have the appearance of pro- 
longations of the stomach. An accessory portion of the liver lies under the 
intestine. The genitalia are as usual in the genus. The spermatotheca is 
empty and crushed, but apparently spherical. The vas deferens is white, 
much convoluted, but not very long. 
This specimen may be regarded as certainly identical with the Tritonia 
cyanobranchiata of Riippell & Leuckart, also found on corals in the Red Sea, 
but must be referred to the genus Marionia on account of the armature of 
plates in the stomach. The external characters and remarkable coloration 
agree fairly well with their plate and description except that the lower parts 
of the branchize are more decidedly yellow. It is possible that it is really 
only a highly coloured variety of Marionia arborescens, Bergh. There are 
considerable differences in Bergh’s description of specimens referred to this 
form, but one of them (‘ Malacologische Untersuchungen,’ in Semper’s Reisen, 
p. 891) does not differ greatly from the animal here examined. It would 
seem that the Tritoniadee of the Red Sea are more brilliantly coloured than 
in other parts of the Indo-Pacific. 
The name Marionia cyanobranchiata has priority over M. arborescens, if the 
two prove identical. | 1 SC Ha 
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