REPORT ON THE CRUSTACEA MACRURA. 839 



carina being sometimes reduced to a narrow thread-like ridge, and each somite has a 

 tendency to be developed into a more or less perfect tooth. 



The telson is long, narrow, tapering, and has the sides depressed. 



The ophthalmopoda are compressed more or less distinctly, and support an 

 ophthalmus that varies somewhat in form and size in different species, and on the inner 

 surface a distinct tubercle that is also variable in different species both in length and 

 importance. 



The first pair of antennae has a short and stout peduncle ; the first joint being 

 excavate on the upper surface and furnished on the outer with a short pointed stylocerite ; 

 the second and third joints are cylindrical and terminally support two flagella, of which 

 the outer is broad and compressed at the base, where it is thickly furnished with 

 membranous cilia, whence it tapers to a fine point. 



The pleopoda are short and two-branched, that of the first pair being developed in 

 the form of a petasma ; the posterior pair has the outer rami, which help to form the 

 rhipidura, without a diaeresis. 



Unfortunately, all the specimens in the collection are more or less injured ; this is 

 the more to be regretted since the genus is one of interest, resembling in many of its 

 characters the genus Benthesicymus, from which it is so widely separated in the form 

 and character of its branchiae. 



The branchial arrangement is given in the following table : — 



Pleurobranehiae, . . . 1 



ArthrobranchL-e, . . . 112222... 



Podobranckin?, . . . 



Mastigobranchia?, . . . 1 r r r r 



hi k 1 m n o 



This genus is undoubtedly the same as Meningodora, Sidney Smith, which that 

 author distinguishes from Hymenodora, Sars, upon a character which at most can be 

 only of specific value, namely, that the coxal plate of the second somite of the pleon 

 is so broad as to overlap the anterior somite. Buchholz's figure of the species (Pasiphae 

 glacial is) that Sars has taken for the type of Hymenodora shows that it is not broader 

 than the coxal plates of the other somites. Mr. Sidney Smith also states that Meningo- 

 dora is laterally compressed, whereas Hymenodora is not, but this difference is one of 

 degree only, since in all the genera of the group lateral compression is a common feature. 



The ophthalmopoda vary somewhat in form in different species that in other respects 

 nearly approach each other, even when they come from distant localities, but in their 

 typical condition they are transversely compressed and furnished with a tubercle on 

 the inner side, which appears to be the rudimentary representative of a larger and more 

 important organ, such as is seen in the deep-sea genera Benthesicymus and Gennadas, 

 belonging to the Dendrobranchiata ; this tubercle is totally distinct from the ocellus 



