172 PERCY SLADEN TRUST EXPEDITION 



Pseudothecosomata*, although we can as yet give no sufficient explanation of these 

 periodical migrations. 



Looking over the foregoing list we may remark that the following species were caught 

 at or near the surface down to 10 fms. 



Limacina injiata, Stat. P, Q, u, v. 



Limacina trochiformis, Stat. P, n, dd. 



Limacina bulimoides, Stat. P. 



Peraclis reticulata, Stat. u. 



Creseis acicula, Stat. P, u, x. 



Creseis virgula, Stat. F, d, dd. 



Styliola subula, Stat. n. 



Hyalocylix striata, Stat. H, n, v. 



Clio pyramidata, Stat. P, d, n, y, ee. . 



Cavolinia longirostris, Stat, x, dd. 



Cavolinia uncinata, Stat. ee. 



Cavolinia tridentata (" Pleuropus longifilis"), Stat. x. 



Cymbulia sp., Stat, d, x. 



Desmopterus papilio, Stat. F, Q, x. 



From this list, if compared with Prof. Stanley Gardiner's list, it may be seen that 

 all these species with the exceptions of Creseis virgula, Hyalocylix striata and Cavolinia 

 longirostris, were caught during the night f; they thus afford another proof of the general 

 rule mentioned above. 



The bathymetric occurrence of Peraclis is worth mentioning : it was found during 

 night at the surface. Formerly I noted a similar circumstance J, though here the exact 

 hour could not be given. More than any other genus of the Thecosomata, Peraclis seems to 

 belong to the mesoplankton. Miss Anne L. Massy § mentions seven specimens of 

 P. triacantha (Fischer) from a depth of — -5 fms, off the S.W. coast of Ireland ; we 

 have here another of the rare instances of the epiplanktonic occurrence of this genus. 



II. HETEROPODA. 



The number of species of this group of pelagic Mollusca is likewise small. By far the 

 greater number of the specimens belong to the Atlantida? or to Firoloida, other genera 

 being very scantily represented, a result which seems to agree with that of the Siboga 

 Expedition. 



Though no new species were obtained, the material enables me to contribute somewhat 

 to our knowledge of little-known species. 



* See for instance Meisenheiiner, I.e. pp. 97 — 99. 



t The hour on which Stat, n was made is not recorded in the list of stations. 

 \ The Pteropoda of the Leyden Museum, Notes Leyden Museum, vol. xxix. p. 202. 

 § The Pteropoda and Heteropoda of the coasts of Ireland, Fisheries Ireland Sc. Inv. 1907, ii. (1909), 

 p. 26. 



