1879.] NATURAL SCIENCES OF PHILADELPHIA. 73 



of them, to be less abundantly distributed through the warm and 

 tropical regions. This seems evident from the information given 

 by Van Hasselt, Kelaart, Alder and Hancock, Collingwood and 

 Pease, as well as by Semper. 1 Tan Hasselt has only three forms 

 of Aeolidiidse, Elliott (Alder and Hancock) four or five, Kelaart 

 nine. Collingwood was rather astonished at the small number of 

 species and individuals which were found on the coasts of China: 

 Formosa, Labuan, and Singapore, and which included no Aeoli- 

 diidse at all. The Pacific seems especially poor in Aeolidiidse, 

 particularly in its northern and eastern part. The exploration 

 of Alaska, under the direction of Mr. W. H. Dall, has only fur- 

 nished five or six forms of this group belonging to the genera 

 Aeolidia, Fiona, Coryphella, Flo.bellina, an d- Hermissenda. 



I. AEOLIDIA, Cuvier. 



Aeolidiana Quatrefages, Ann. Sci. Nat. Zool., Ser. i, t. iii. p. 134, 1844. 

 Aeolidia (Cuvier), R. Bergk, Anat. Bidr. til Kundsk. om Aeolidierne, 



Danske Vidsk. Selsk. Skr. 5 R. vii. 1864, p. 199. 

 Aeolidia, R. Bergh, Beitr. zur Kenntn. der Aeolidiaden, I. Verh. der R 



K. zool.-bot. Ges. in Wien, xxiii., 1873, pp. 618-620; ii. 1. c. xxiv. 1874, 



pp. 395-396. 



Corpus sat depressum, rhinophoria simplicia, papilla? 2 caducse, 

 compressae. Podarium antice angulatum mandibular applanatae, 

 processu masticatorio non denticulato. Radula dentibus uniseri- 

 atis, regulariter arcuatis, pectiniformibus instructa. 



This genus is easil}' distinguished by its depressed form, the 

 simple rhinophoria, the flattened papilla?, and the straight front 

 margin of the foot, with nearly rounded edges. The mandibles 

 are rather short, very much flattened, the cutting edges simple ; 



Mcnke), Eolida, Eolidia, and Aeolidia by different authors. It may be 

 best, as I have done for many years, to adhere to the original Cuvierian 

 way of writing it. Cf. my Unders. af Fiona atlantica, Natur. Hist. Foren. 

 Vdsk. Meddel. for 1857, p. 276, 1858. 



1 Cf. my Malacol. Untersuch. (Semper, Reisen ira Archipel. der Philip- 

 pines II. ii.) Heft 1, 1870, p. 1. 



2 I always use the term papilla instead of the more usual one of brancliw 

 or cirrhi, partly because it is the Linnean term, partly because the organs 

 do not exclusively serve for respiration, which is partaken of by the whole 

 surface of the skin, that over the papilla? as well as elsewhere, among all 

 the N udilranchiata. 



6 



