244 Transactions of the Society. 



corona is pretty well retracted and the head-sheath fully extended. 

 The jaws are relatively large and elongated. 



This is a case in. which the most careful drawings fail to 

 explain themselves. The keel is so extensive that no boundary 

 lines can show its real form. By much turning of the animal 

 under the cover-glass I ascertained that it was in the form of a 

 volute. The diagram (fig. lid), which is a supposed optical section 

 through the middle of the body, illustrates its structure as 

 accurately as may be. 



The study of the living animal was made while travelling, and 

 with limited time. I hoped to find more specimens among the 

 preserved material from the same pond, but, after the most careful 

 search, failed to find one. 



Habitat. — Water-lily pond on the Praia at Gloria, Eio de 

 Janeiro; two examples seen, April 1912. 



Rattulus braziliensis sp. n. Plate X, figs. 16a, 16b, 



S2yecijic Characters. — With two short keels, varying from one- 

 fourth to one-third of length of contracted lorica ; toe longer than 

 lorica ; largest substyle one-third of toe, diverging widely from it. 



General Description. — Contracted lorica, 120 yu, in length, toe 

 150 fi, keels about 40 [x, largest substyle 50 fx, two shorter about 



lOyLt. 



The body is broadest just behind the keels, and tapers to the 

 foot. The keels are strongly rounded. The toe continues the 

 line of the long axis of the body, and is gently curved, with a 

 sudden sigmoid bend at the base. The substyle springs from the 

 left side of the toe, but immediately crosses to the right, and 

 sticks far out. 



It is only necessary to compare the species with the two which 

 have double keels. R. bicristatus has much longer keels, and R. 

 mucosus has longer keels and a much broader body. R. braziliensis 

 differs from both in the conspicuous substyle. (See Jennings, 13). 



Habitat. — Water-lily pond in Pra9a Eepublica, Pdo de Janeiro, 

 April 1912. About a dozen examples seen. 



Polychsetus collinsi Gosse. Plate X, fig. 15). 



Type in pond in Botanic Gardens, Eio de Janeiro. 



Variety. — Spines as in the type, but an additional pair on the 

 second segment of the foot. Lorica dotted, margin plain, without 

 the usual fringe of short spines. 



Appears to have some claim to specific rank, perhaps rather 

 more than P. sericus Thorpe, but it would be necessary to study 

 other examples, and I only found one. 



Habitat. — Marsh beside the salt Lagoon, Eio de Janeiro. 



