37 



bear small spiniform processes on their outer margin. In Splicer, dispar (pi. IX, fig. 3 h) and 

 in Sphtsr. insignis (pi. X, fig. 1 b and fig. 1 c) the frontal plate expands in a most peculiar 

 way. Seen from below, the head tapers very much towards the front, whereupon it dilates 

 to an almost circular plate or a transverse oval with acute lateral angles; the sides and the 

 front margin of the circular plate and the front margin of the oval project into a series of 

 closely situated spiniform little processes ; on the ventral side of the plate we see a chitinous 

 ring, from the inner edge of which four processes run towards the centre; in S. dispar these 

 processes do not meet, but form the surroundings of a cross-shaped space, whereas in S. insig- 

 nis they meet in the centre, thus forming a cross, and dividing the space into four parts, 

 (which perhaps are pierced with small holes). The purpose of this peculiar ring is un- 

 known to me. 



The part surrounded by the protruding frontal and lateral borders frequently lies 

 very deep, and where the lateral borders are high, sometimes, as in Splicer, curtipes (pi .X, 

 fig. 2f and fig. 2 g), they hide the rostrum and the maxillae, if the animal is seen from the 

 side; as a rule a lateral view shows these organs in almost their whole, or in half of their 

 length. Several males of the same species may show great individual difference in this 

 point, whereas on the other hand, there are species, as e. g. Splicer, curtipes, in which the 

 rostrum and the maxillae are always partly invisible because of the height of the lateral 

 borders, in other species again, as in Sphcer. microcephala (pi. VIII, fig- 2 g and fig. 2 h), the 

 borders are so low, that the above-mentioned organs are always visible in nearly their 

 whole length. 



The sub-median skeleton, which is found in all females and has been described as 

 far as this sex is concerned, is also seen in all males, aud in most respects shows a similar 

 structure, but in most species of the genus Sphceronella it is produced into free processes. 

 Three pairs of such processes may be found. Those of the first pair are usually rather short 

 and broad, sometimes rounded, in S. microcephala (pi. VIII, fig. 2 g and fig. 2 h, i) pretty 

 long, slender and pointed, being situated behind or below the basis of the maxillae; some- 

 times, as in S. elegantula (pi. II. fig. 2 f and fig. 2 g), they extend backward over the basal 

 part of the maxillipeds. The second pair of processes are found most frequently, and may 

 become much longer than any of the other two pairs; they proceed at a shorter or longer 

 distance from each other between the maxillipeds, and are sometimes parallel, sometimes or 

 mostly diverging. The third pair appears in very few species only, as in S. paradoxa 

 (pi. Ill, fig. 4 h and fig. 4 i), in S. Metopw and in S. Holb0lli (both on pi. V.) ; they proceed 

 between and a little behind the second pair and are much shorter than these ones. In the 

 systematic description of the species I use the terms: first, second and third pair, in speaking 

 of these processes. 



The Antennulm are found in all species ; in Stenothocheres they are situated in front 

 of and outside the antennae, in all other forms they are found on the lateral margins of the 

 head, where these merge iuto the frontal margin. They are constructed much like those of 



