630 " THETIS " SCIENTIFIC RESULTS. 



Jackson, were very numerous. So also were those procured by 

 tlie "Thetis" Expedition at the neighbouring stations of Port 

 Hacking and Botany Bay. At all three localities there were 

 many females, with brood pouches, but no larvse in them. That 

 the two forms cannot be united will, I think, be made clear by 

 the following comparison of their characters. 



In the earlier species the body has a pair of dorsal spines at 

 the end of the first peraeon seguient, a similar pair on the middle 

 of the second segment, which also carries a spine over the base of 

 each of tlie second gnathopods, thus furnishing to the adult male 

 the six spine-processes to which the specific name refers. The 

 first pair is wanting or feebly developed in the female and young 

 male. The new species has a dorsal pair at the end of the first 

 segment, one in the middle, and one at the end of the second, and 

 two other pairs, arming respectively the third and fourth segments 

 at the middle. It is to tliese ten processes in a continuous line 

 of pairs that the name decacentruvi alludes, without taking into 

 account the lateral processes which are difficult to see even over 

 the second gnathopods , and still more in position far below the 

 first and fifth dorsal pairs. Here also the female has a smaller 

 apparatus, the first and fourth segments having lost their arma- 

 ture. On the second se^jment moreover the first pair is moved 

 forward in correspondence with the altered position of the second 

 gnathopods in the female sex. 



Mayer describes the first antennae in his species as very long, 

 especially in the male, and with curved basal joints ; the flagellum 

 in both sexes seven-jointed, the first joint in the male being 

 relatively very long; flagellum of the second antennae in the male 

 five-jointed, in the female four-jointed. The new species agrees 

 in so far that the first antennae are very long, and in the male the 

 last joint of the peduncle is commonly longer than the penulti- 

 mate, whereas in the female those two joints are subequal, but in 

 both sexes the number of joints in the flagellum, though very 

 variable, may ascend far beyond seven. In one female specimen 

 it contained nineteen joints, in a male specimen seventeen, the 

 joints slender and elongate, the first always the longest. Some- 

 times the basal joints of the peduncle show a slight curvature, but 

 often they are quite straight. The slender flagellum of the second 

 antennse is usually seven-jointed, but may be eight-jointeil. 



For the fringing spines of the third joint in the mandibular 

 palp Dr. Mayer gives the numbers 1 -}- 1 1 + 1, In two examined 

 specimens of the new species the number is 1 + 14-H 1 and 1 + 15 

 + 1. Such minutiae, however, are very likely to be subject to 

 much variation. Dr. Mayer notes that the third joint of the 

 niaxilliped palp has distally a process. Such a process is present 

 also in our species, but it is very small. 



