194 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 15 



constructed longitudinal view of the everted apparatus is given in fig. 14. 

 The figure indicates that the two prostatic vesicles are included in the 

 eversion but the major part of the seminal vesicle remains in the body. 

 The seminal vesicle is cut obliquely; actually it is a long oval body. 



Remarks — Prosthiostomum parvicelis is apparently one of the more 

 common polyclads of the Galapagos, as the present specimens came from 

 a different island than the original finding, which was in Sullivan Bay, 

 James Island. 



Faunistic remarks 



While the present collection can hardly be supposed to exhaust the 

 polyclad fauna of the islands, it is suggestive. For instance, one is sur- 

 prised at the absence of typical cotyleans, such as pseudocerids and eury- 

 leptids, usually a common element of the polyclad fauna of tropical and 

 subtropical regions ; and the absence of stylochids, which are also usually 

 characteristic of warm waters, is noteworthy. A certain resemblance is 

 apparent to the polyclad fauna of southern California and Lower Cali- 

 fornia (Hyman, 1953). For instance, a latocestid is perhaps the com- 

 monest polyclad of the Gulf of California. A species of Cryptocelis, in 

 which the details of the prostatic vesicle are closely similar to those of 

 C. insularis, is found off southern California. A Prosthiostomum, so 

 much like P. parvicelis that some doubt still remains of its specific differ- 

 ence from the latter, is common along the shores of southern California. 

 As planocerids tend to be cosmopolitan, comparison of the planocerids of 

 the two regions is not profitable; but it might be noted that all four 

 planocerids found on the Californian and Mexican coasts have large teeth 

 in the cirrus sac, as in the two Galapagos species. Possibly the develop- 

 ment of large teeth in the cirrus sac is related to the tropical habitat. 



Summary 



In three different collecting trips of the Allan Hancock Pacific Ex- 

 peditions to the Galapagos Islands, there were collected a total of five 

 different polyclad species, four of them new, namely, one latocestid, 

 Latocestus galapagensis; one cryptocelid, Cryptocelis insularis; two 

 planocerids, Planocera tridentata and Aquaplana oceanica; and one 

 prosthiostomid, Prosthiostomum parvicelis Hyman, 1939. Some similarity 

 is noted between the Galapagos polyclads and those of southern Cali- 

 fornia and Lower California. 



