REPORT ON THE CRUSTACEA MACRURA. 375 



parallel margins, the outer margin being produced to a long blunt tooth at a distance 

 from the extremity, and the inner fringed with long hairs that are rather distantly- 

 separated. 



The gnathopoda and pereiopoda are biramose and tolerably advanced in development. 



The pleopoda are developed on the third, fourth, and fifth somites as unequally 

 biramose, saccular appendages, but I could not detect any on the first two somites ; those 

 of the sixth are large and well formed, and have the tooth on the outer margin of the 

 outer plate situated about halfway between the apex and the base. 



JIastigojnis dorsispinalis (PL LXV. fig. 3). 



The next stage in which I am able, with the specimens at my command, to trace the 

 progressive development of the short telson form, is in that which Claus has named 

 Mastigopus. In the Challenger specimens in this stage also, as previously in Acantho- 

 soma and Elaphocaris, there appear to be more than one species represented. 



The carapace, not including the rostrum, is rather less than a third of the length of 

 the body of the animal. The rostrum is about half the length of the carapace, and 

 unarmed ; a small but strong tooth stands at the outer angle of the orbit, and another 

 on each side slightly posterior to the gastric region. 



The pleon has the posterior margin of the dorsal surface of each somite armed with 

 a strong tooth, but the posterodateral angles are smooth and rounded off, except the 

 fifth and sixth, which are produced to a small tooth. The sixth somite is quite as long 

 as the two preceding. 



The telson is about half the length of the sixth somite. 



The ophthalmopoda are subequal in length to the rostrum. The ophthalmus is broader 

 than the stalk, which narrows gradually to the base. 



The first pair of antennas has the peduncle three-jointed. The first joint is long and 

 slender, broad at the base for the reception of the otocyst, and armed on the outer side 

 with a sharp, stout tooth, whence it suddenly narrow's and continues cylindrical to 

 the distal extremity, where it supports the second joint, which is about half the length of 

 the first and a little longer than the third, and this, in turn, supports a flagellum about 

 as long as the peduncle, and a small, secondary, single-jointed branch. 



The second pair of antennas has the flagellum broken off at the peduncle ; it carries 

 a long, narrow scaphocerite, subapically furnished with a sharp tooth on the outer side, 

 and fringed with hairs on the inner. 



The first pair of gnathopoda has so far assumed the adult character in having the 

 carpos curved at the meral extremity. 



The second pair has also much of the character of those of the adult animal ; the first 

 three or four joints being robust, and the two terminal ones slender and feeble. 



