108 MARINE FAUNA OF ST. ANDREWS. 



Fam. 3. Mesostomea, 0. Schm. 

 Genus Mesostomum (Dugfes),M. Sch. 



Mesostomum htfidum, n. sp. 

 [Plate VIII. figs. 3-6.] 

 Oil the under surface of stones from low-water mark, East 

 Rocks. One tentli 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 papillaj on their crenated 

 edge ; these pajsiUae 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, ffirst. 



Genus Vortex, Ehrenberg. 



Vortex capitata^ OErst. 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 flustrce of Dalyell. It is 

 abundant under stones between tide-marks. 



Monocelis rutilans, O. F. Miiller, Zool. Danic. iii. p. 49, 

 tab. 109. f. 10 & 11. 



Occasionally in the laminarian region. 



