REPORT ON THE CRUSTACEA MACRURA. 



125 



Fio. 30. — Eryoneicus coecus. After a drawing by von Wille- 

 moes-Suhm. a 1 , first antenna ; a 2 , second antenna ; 

 p 1 , p 2 , p*, p*, 2^, pereiopoda ; st, stomach ; t, testis (?) ; 

 i, intestinal canal. 



The pleon has similar spine-like teeth on each somite, both laterally and in the 

 median line. 



The telson is spinous, and has the terminal extremity beautifully fringed with hairs. 



The branchiae I have not been able to enumerate with certainty, but they exist 

 rather in an impoverished than in a developing, condition ; the central stalk- is long 

 and robust, while the lateral filaments exist 

 as globular papilla?, diminishing gradually from 

 the base to the extremity, and are of less length 

 than the diameter of the stalk to which they 

 are attached. 



The possibility has occurred to me of its 

 being a young and immature form of some 

 species allied to Polycheles, a hypothesis that 

 was supported by the bottle containing it being 

 labelled " Zoasa of Brachyura," but there are 

 certain features that seem to be opposed to 

 this supposition. 



The brephalos of Willemcesia has not 

 been observed, but I have been able to 



determine by examination of an embryo in an advanced condition (PL XX. fig. 2), that 

 the ophthalmopoda at that period are well developed, and I have no doubt that when it 

 quits the ovum the brephalos is in the megalopa stage, with the ophthalmopoda 

 developed as in the young of Astacus. But the specimen that I have before me has no 

 ophthalmopoda or trace of one. The frontal margin on each side of the median line, 

 in the place where the ophthalmopoda are situated in the normal species of Astacidea, 

 is slightly excavate, and this is suggestive of an orbital impression, but there is not 

 the slightest trace of an organ of vision here, but on the outer side of the frontal margin, 

 beyond the position of the antennae, and corresponding with the ophthalmopoda in 

 Willemcesia, is a dark circular spot that is suggestive of being such an organ, but 

 without any structural indication of its function. 



The first pair of antennas differs from that in Polycheles and in Willemaesia in not 

 having the inner margins, from the base to the distal extremity of the first joint, 

 produced laterally so as to be brought into contact with each other and elevated upwards 

 into a crest-like form, but only a large spine-like tooth at the inner distal angle. 



The second pair of antennas is peculiar, and, so far as I know, unique in character. 

 The first or coxal joint carries a phymacerite, developed in the form of a long, 

 straight, cylindrical tube that is obliquely truncate at the distal extremity. If we 

 examine the same organ in Willemcesia we shall find it, though different in form, to be 

 analogous in character, since it consists of a long cylindrical organ, but so curved that, 



