492 
W. T. CALMAN. 
eye-stalks. Seen from the side, the lower margin is concave 
in its anterior two-thirds, and in this part it overhangs the 
bases of the mandibles and maxillulae in a very slight pleural 
fold. On the side of the head a shallow groove, most clearly 
seen in a specimen treated with caustic potash, runs obliquely 
upwards and backwards, becoming almost imperceptible 
where it joins with its fellow across the dorsal surface. At its 
lower end, where it lies immediately above the basal articu- 
lation of the mandible, the integument along the floor of the 
Bathynella natans, $ . Head and anterior thoracic somites, 
lateral view. a'. Base of antennule. a". Base of antenna. 
md. Mandible, m. gr. Mandibular groove, mt. Metastoma or 
lower lip. wx'. Maxillula. mx" . maxilla. thp\ Appendage 
of first thoracic somite. I, II. Tergites of first and second 
thoracic somites. 
groove is slightly thickened and stiffened, and this thickening 
spreads a little way in front and behind along the margin of 
the pleural fold. The significance of this “ mandibular 
groove ” is discussed below. 
Telson. — The sixth abdominal somite is deeply incised 
behind in the middle line where the anus opens, and on either 
side of the incision, towards the dorsal side, a short appen- 
dage is articulated, subcylindrical . or slightly flattened, and 
Text-fig. 2. 
TTi.gr. 
II. 
I . 
