34 THE VOYAGE OF H.M.S. CHALLENGER. 



series of lobes, arranged in two rows running from the base to the apex of the plume : 

 those at the base are long, broad, flat, and foliaceous ; those near the apex are slender, 

 rounded, and digitiform. 



In the second pair of pereiopoda the arthrobranchial plume approximates more nearly 

 to the form which exists in Callianassa, that is, of two longitudinal rows of long and 

 slender plates compressed closely against one another ; but as these plates approach the 

 extremity of the plume, they lose the flattened or compressed con- 

 dition, and have a more cylindrical appearance. 



In Cheramus occidentalis the arthrobranchia attached to the 

 first pair of pereiopoda consists of a double row of long fiat plates 

 which gradually become narrow and slender, rounded and digitiform, 

 lessening in length as they approach the apex of the plume — as 

 shown in the accompanying woodcut. 



In one instance on the posterior arthrobranchia a process had 

 Fm. 2.— Arfhrobranohia of commenced as a broad and flattened plate, and then became 



Cheramus ucaaentalis. x 



compressed into a narrow cylindrical continuation, showing, I think, 

 very clearly that the two kinds of branchias are but modifications of the tricho- 

 branchiate type. 



Scallasis, 1 n. gen. 



This genus resembles Cheramus, but differs in the form of the eye. The ophthal- 

 mopod, or peduncle of the eye, is globular, with the eye at the extremity. Second 

 pair of gnathopoda pediform. Posterior pair of pereiopoda minutely chelate. Branchia 

 arranged in two rows on a stem, subcylindrical filament slightly if at all compressed. 

 Pleopoda carry a moderately-sized stylamblys. Marginal hairs ciliated and multi- 

 articulate. 



Scallasis amboinse, n. sp. (PI. II. figs. 3, 4). 



Carapace smooth. Rostrum small and sharp ; cervical groove well defined. Telson 

 quadrate ; posterior margin slightly excavate, fringed with cilia, and having a small 

 rudimentary pointed tooth in the median line. 



Length, 12 - 5 mm. (half an inch). 



Habitat. — Taken at Amboina, one of the Celebes Islands, on the 6th of October 1874. 



The only specimen taken is very imperfect. The few limbs preserved are the anterior 

 antenna and one of the posterior pair of pereiopoda. Therefore, in giving a description, 

 1 am compelled to refer to the only parts that have not been lost, and these may not be 

 of great specific importance. 



1 2».«ax«, to scrape ; A;i(, mud. 



