Page 273. 
94 THE TELSON OF THE MACRUROUS CRUSTACEA. 
slender, and composed of a central and two lateral elements, which 
are fixed to the sides of the dorsal shield. 
The seventh segment, or telson, consists of a distal fin and a proxi- 
mal calcified portion. The fin is azygos, semi-elliptical, and supported 
on rays, like the exo- and endo-podites of the sixth segment. It also 
resembles them in having two lateral elongated calcified masses at its 
margins. There is no median separation. 
The calcified portion consists dorsally of a small semicircular cen- 
trum or dorsal shield, which is close under the dorsal plate of the 
preceding segment, and is separated from the lateral masses by a 
marked groove, not by an articulation. 
These lateral masses are each distinctly separable into three parts: 
1st, a thin longitudinal one, which approaches the sixth dorsal plate, 
and ends posteriorly in a sharp spine. 
Internally it comes in contact with the next, the 2nd part, which 
latter joins the azygos centrum at its antero-internal margin, and at 
its distal end gives attachment to the 3rd part. Beyond the centrum 
there is a considerable interval between the two lateral masses dorsally. 
The 3rd part consists only of a free spine, directed backwards and 
articulated to the 2nd. It rests on the azygos fin. : 
Ventrally this segment presents only a short transverse bar, in 
front of the anus, composed, as in the preceding one, of a central and 
two lateral portions. 
On the supposition that this seventh segment is a true one, the ~ 
small dorsal centrum corresponds with the much larger one in the 
other segments, while the swimmerets are represented by the lateral 
masses described above; the 2nd part of which corresponds with the 
propodite, and the lst and 3rd with the exo- and endo-podite respec- 
tively, each bearing spines, and connected with the propodite and 
with the fin. 
The short transverse ventral bar corresponds to the narrow cen- 
trum, and is composed of the portions, as in the preceding segment. 
I have no means of telling whether it is laterally connected with the 
dorsal shield. 
The position of the anus behind this seventh transverse bar is 
strongly in favour of the alimentary canal being segmentally terminal, 
although this condition is disguised by the coalescence of the lateral 
appendages above, which consequently makes the anus ventral. 
If the above explanation is accepted with regard to this particular 
species, it is highly probable that it is true in those allied to it, and 
would then refer to the lobster and cray-fish. Professor Rolleston 
says of the latter,* that the proximal segment of the telson is not 
* “ Forms of Animal Life,” 1870, p. 95. 
