144 DR. J. ANDERSON ON SACCULINA. [Feb. 7, 



Dorsal fin low, small, pointed, falcate, and situated near the ter- 

 mination of the posterior third of the body; pectoral flipper sub- 

 triangular, pointed and emarginate posteriorly. 



Uniform dirty white *. 



Skull rather flat posteriorly, broad in front ; rostrum short, 

 broad at the base and not much tapered ; dentition -j-f. 



Hab. The deep channels of the Irrawaddy river, Burmah, from 

 300 to 900 miles from the sea. 



10. Note on the Occurrence of Sacculina in the Bay of 

 Bengal. By John Anderson, M.D., F.L.S., F.Z.S., 

 &c, Director of the Imperial Museum, Calcutta, and 

 Professor of Comparative Anatomy, Medical College, 

 Calcutta. 



[Keceived February 7, 1871.] 



Some twelve years ago I directed attention to the not unfrequent 

 occurrence of those remarkable forms of parasitic Crustaceans Saccu- 

 lina and Peltogaster -f on the common shore-crabs of these islands, 

 Carcinus mcenas and Pagurus bernhardus. These peculiar types of 

 parasitic life have been lately referred by Fritz Muller to a new 

 group, which he has designated Rhizocephala. Since my residence 

 in the East, I have collected marine Crustacea on a large scale, and 

 have critically examined all the species which would have been 

 likely to yield these most iuteresting parasites, but have succeeded 

 in finding only one species infested by them, and that to the exclu- 

 sion of Peltogaster. The Crab (Thalamita crenata) which yielded 

 Sacculina is the common swimming species of the rocky shores of 

 the islands and coast of the Bay of Bengal. I have been fortunate 

 enough to obtain only one specimen of the parasite. There is 

 nothing in its outward appearance by which it can be separated 

 from the species which is so prevalent ou Carcinus mcenas along our 

 coast — a fact of great interest so far as it relates to the geographical 

 distribution of these forms of life, provided that further investi- 

 gations into the postovular development of the species verify its 

 identity with the European form. In connexion with this, it is 

 curious to note that while Peltogaster has been found hitherto only 

 along the Danish and eastern and western coasts of the British Isles, 

 Sacculina was first discovered by Cavolini on the shores of the 

 Mediterranean. Further research may reveal the occurrence of the 

 latter in the waters of the Red Sea. 



The specimen of Thalamita crenata which yielded Sacculina was 

 received from the Andaman Islands, in the Bay of Bengal. 



* I am indebted to Captain Bowers for our specimen of this Cetacean, and 

 for tbe description of its colour when recently dead. 



t Proc. Eoyal Physical Soc. Edinb. 1854, lviii. pp. 412-415; Ann. & Mag. 

 Nat. Hist. 3rd ser. vol. ix. p. 12 et stq. pi. i. 



