108 
MARINE FAUNA OF ST. ANDREWS. 
Fam. 3. Mesostomea, 0. Schm. 
Genus Mesostomum (Dugbs), M. Sch. 
Mesostomum bifidum , n. sp. 
[Plate YIII. figs. 3-6.] 
On the under surface of stones from low-water mark, East 
Rocks. One tenth of an inch long, and of a very pretty pale 
orange hue. The body is pointed anteriorly, dilates in the 
middle, and diminishes posteriorly, terminating in two pro¬ 
cesses which have a few rather large papilke on their crenated 
edge; these papillae seem to have a slight sucker-action. 
There are two semilunar eyes, with the concavity external. 
The cilia are specially distinct a little behind the snout, on 
each side, at points corresponding to the long ciliary whips of 
the developing Nemertean. The male organ formed a spirally 
marked conical process behind the large median sucker; and 
the testes were loaded with spermatozoa in various stages of 
development. 
Fam. 4. Derostomea, (Erst. 
Genus Vortex, Ehrenberg. 
Vortex capitata , (Erst. Entwurf Plattwiirmer, p. 65, 
pi. 1. f. 7. 
[Plate VIII. figs. 7-10.] 
Occasionally under stones between tide-marks. Many dia¬ 
toms occur in the digestive canal. 
Fam. 5. Opistomea, O. Schm. 
Genus Monocelis, Ehrb. 
Monocelis unipunctata (Fab.), (Erst. Ent. Plattw. p. 56. 
This appears to be the Planaria jlustrcc of Dalyell. It is 
abundant under stones between tide-marks. 
Monocelis rutilans , O. F. Muller, Zool. Danic. iii. p. 49, 
tab. 109. f. 10 & 11. 
Occasionally in the laminarian region. 
