1906.] OF souriiEii^'T ijstdia and ceylon. 677 



Bergli in his ' Sj^stem ' mentions 19 species of Pleuroijliyllidia. 

 Of these I think that P. onarmorata Kelaart is probably Linguella 

 cinerea Farran, though the description is somewhat vague. 

 P. luguoris Bergh seems to have been accidentally omitted from 

 the list. Only two species appear to have been described since : — 



20. P. rosea Bergh. 



21. P. stenidia Bergh. 



To the five species of Linguella enumerated by Bergh [l. c.) may 

 be added : — 



6. L. variolosa Bergh. 



7. L. cinerea Farran. 



(? = Di2:)hyllidia inarmorata Kelaart.) 



Camarga., represented by one species, C. marginaia (Oersted), 

 from the Pacific Coast of Nicaragua, seems to have a ridge in 

 front of the rhinophores connected with the mantle by a wide 

 commissure*. 



The genus Pl&urophyllidiella was proposed by me (Proc. Zool. 

 Soc. 1903, vol. i. p. 250) for a species, P. horatii, from East Africa, 

 M^hich appears to have no traces of branchi?e or a branchial cleft, 

 though lateral lamellse are present. The head parts appear to be 

 as in Linguella. Bergh (Siboga, 1905, p. 208) suggests that the 

 branchicie may be so deeply retracted as to be invisible. I doubt 

 if this is the case. If the branchise are merely obscured and not 

 really absent, the more probable explanation is that they are so 

 far from the body that they are undistinguishable from the lateral 

 lamellae, which is much the same as saying that they have 

 disappeared if the conformation described exists in the living 

 animal. While fully admitting that the preserving fluid may 

 strangely distort external features, I see no particular reason to 

 suspect this specimen f. 



In several Pieurophyllidias (especially P. pallida, P. com/)i«, and 

 P. stenidia) the lateral lamellfe are greatly reduced : in Pleuroleura 

 both branchise and lateral lamellfe are entirely absent. The 

 radula of Pleuroleura is narrower than in the other genera, and 

 in one species {P. 2ncteti) there are only four laterals. The head 

 parts seem to be as in Linguella, though the plates show some 

 discrepancy in this respect, probably due to distortion in preserved 

 specimens. Some of the species are quite small, and none seems to 

 exceed about 3 centimetres in length. Probably the total absence 

 of a specialised breathing-apparatus is unfavoui'able to the growth 

 of large molluscs. It is hard to say whether the genus should be 



* I am not sure that I clearly understaiid Bera;h's dia2;nosis of this genns, and the 

 figures in his Monograph on the Phyllidiadas (pi. ix.) do not throw much light on 

 the external characters. The diagnosis is:— "Corpus minus elongatum. Cb^peus 

 ten taculai'is latus, semilunaris, angulis productis; caruncula nuchalis humilis, lata, 

 in jiallium commissura latiore transiens ; rhinophoria sejuncta. Sacci enidogeni 

 nulli." 



t In my description, p. 252, 7. c, the statement that the first lateral tooth bears 

 denticles " only on the internal side " is a misprint : read " external side." 



