20 DR J. STEPHENSON ON 
In length most specimens were from one-third to two-thirds of an inch, some few 
longer, some even shorter; they agreed therefore rather with BUrerr’s Naples 
specimens (scarcely more than 1 cm.) than with Maclnvrosn’s (1-14 inches). In 
breadth they were about 1 mm. ‘They were thus relatively short, and sausage-shaped ; 
the posterior end was narrower and somewhat pointed. The animals are active, can 
swim freely, and are very hardy and resistent under examination. 
Green and yellow are noted by previous authors as being the usual colours; JouBIN 
(8) adds white and red. In my specimens the range of colour was extensive—yellow, 
light orange, light greyish yellow, light brownish grey, light brown; one specimen was 
noted as being between pink and brick-red, the colour being due to the intestine. A 
green specimen, almost certainly of this species, was given me one evening by Dr A. L. 
Kine. I was just leaving the laboratory, and deferred a detailed examination ; but the 
animal, which was damaged, had disintegrated before the next day. ‘The head, or the 
tail, or both, are lighter in tint, and the margins of both head and body are more trans- 
lucent. The ova may appear as very marked yellow masses in a row on each side of the 
middle line. 
Certain markings on the head deserve notice. MacInrosu has described a pale 
streak in the median line anteriorly ; and has noted that in some individuals a few 
white grains are to be seen between the anterior pair of eyes. BUrcEr, however (3), 
found no pigment spots or streaks on the head. In the Millport specimens there may 
be a pale streak in the middle line in front of the eyes ; certain specimens, again, show a 
pair of white splashes, each a collection of minute white specks, between and in front 
of the anterior pair of eyes; while others show a pair of dark pigmented patches, 
elongated in shape, broader anteriorly, one on each side of the dorsal surface of the 
head, stretching from the anterior to the posterior eye; but none of these markings on 
the head were constant. 
The shape of the head is much used in this genus as a means of discriminating the 
various species. MaclInrosu describes it as being wider than the succeeding part of the 
body, Birger as being broadened and of an elongated egg shape. I have found it as 
a rule a somewhat short oval, sometimes rather flattened in front, occasionally shorter 
and almost circular in shape; it is slightly—sometimes very slightly—broader than 
the succeeding part of the body, from which it is marked off by a constriction ; there is 
a slight median notch with well-marked cilia in the middle line anteriorly. 
The eyes, in this genus four in number, are, according to MacINnrosu, set in a square ; 
according to BURGER, they are very small, and are set in a rectangle. In my speci- 
mens they were arranged in a rectangle, the side lines of which were as a rule distinctly 
longer than the front and back; occasionally, in an animal with shorter and more 
circular head, they formed a square. They were, for the size of the animal, large and 
conspicuous; and in one specimen the anterior pair were rather larger than the 
posterior. 
The cephalic grooves are one pair, which notch the margins of the head in front of 
