OCR Text |
Show 110 MR. F. E. BEDDARD ON ISOPODA COLLECTED [Feb. 2, widens out laterally ; the ridge is concave forwards, dorsally, and closely embraces a median oval convexity which lies in front of it; the fourth thoracic segment has a row of short tubercles, arranged in a semicircle with the concavity directed forward, on the ventral surface. Of the three posterior thoracic segments the first is the largest, the second and third being smaller and subequal; each of the segments is traversed dorsally by a strong ridge, which is tuberculate ; the first of these segments has a number of short tubercles scattered over the ventral surface, and the two succeeding segments are ridged in the same region. The segments of the abdomen are comparatively smooth, being only slightly roughened laterally. The abdominal shield is smooth with the exception of the lateral margins, which are serrate; it terminates in a short median spine. The thoracic appendages are tuberculate on the proximal joints ; the uropoda bear a single median longitudinal row of tubercles. Station 174 ; 600 fathoms. 7. ARCTURUS SPINOSUS, n. sp. This is the largest of the deep-sea species, measuring up to 48 millim., the antennae measure 60 millim. The males differ slightly from the females, the latter being wider in the thoracic region and more spiny. The anterior margin of the head is excavated ; between and a little in front of the eyes are a pair of long spines, behind these are a pair of shorter spines ; in the female there is an additional pair of spines situated outside these latter. Of the first four thoracic segments, the fourth is slightly the longest in the male; in the female all four are subequal. On the first three thoracic segments, the posterior ridge bears three pairs of long spines situated at equidistant intervals ; the fourth thoracic segment has only two pairs, but the epimera have each a long spine, wanting in the anterior segments. In the female the first thoracic segment has four pairs of spines, the other segments being as in the male; between these principal spines there are, however (in the female), numerous smaller spines, and the margins of the epimera are furnished with short spines; each of these segments has in both sexes an anterior ridge covered in the male with blunt tubercles, in the female these tubercles are pointed. Of the three posterior thoracic segments the first is the longest; the posterior ridge is tuberculate, the tubercles being more strongly marked in the female ; the epimera of these segments have a large lateral spine. The three first abdominal segments are distinct; the last free segment has a long lateral spine on either side in the female. The abdominal shield terminates in a single median spine, and in two longer upwardly curved lateral spines. The surface of the abdominal shield is tuberculate in the male and covered with short spines in the female ; in this sex there are in addition a pair of moderately long lateral spines, situated just in front of the posterior lateral spine. The thoracic appendages in the female have a few short spines; in the male only the three last pairs are thus provided ; the uropoda are tuberculate. Station 146; 13/5 fathoms. |