MORPHOLOGY OF BATH YN ELLA. AND ALLIED CRUSTACEA. 503 
thoracic region instead of seven as described by Vejdovsky. 
This conclusion is fully confirmed by Chappuis and the 
character is so unusual that it deserves further consideration. 
I formerly stated (1899, p. 342) that “Nebalia and some 
Stomatopods ” agreed with Bath ynella in having the first 
thoracic somite free from the head. As regards the Stoma- 
topoda, this statement was based on a remark of Claus, 1 2 which 
appears to be true only of the larvae. No adult Stomatopod 
has the tergites of the first or second thoracic somites free 
from the carapace, while those of the third and fourth are 
only indistiuctly represented. 3 * * * 
InNebalia, the carapace envelops, but remains free from, 
the thoracic tergites. The grooves separating these from one 
another are distinct, but the anterior limit of the first tergite 
coincides with the line along which the free carapace passes 
into the dorsal integument of the head-region, and it is not 
possible to say that the first tergite is defined from the head 
in the same way as it is from the following tergite. Owing to 
the small size of Nebaliait is difficult to obtain a clear view 
of the parts in question, but it is comparatively easy to do so 
in the case of the large Mysidacea of the genus Gnatho- 
phausia, in which also the first thoracic somite has been 
stated to be distinct from the head. 8 
If the free portion of the carapace be cut away on one side 
of a specimen of Gnathophausia (Text-fig. 12) the tergites 
1 “ Bei den Squilliden bleibt iibrigens die ganze Region der Kiefer- 
fiisse vom Ruckenschilde getrennt, das Segment des ersten Kieferfusses 
gelit hier nnterlialb der Schildplatte in die Innenlamelle fiber ” (Claus, 
1876, p. 53). 
2 Giesbrecht (1910, p. 9, pi. ii, fig. 9) states that the structures here 
regarded as the tergites of the third and fourth somites represent 
respectively the tergites of the first and second and of the third and 
fourth somites fused together, but it is not clear on what evidence this 
statement is based. 
3 “In Sars’ figure of Gnathophausia longispina . . . the 
first thoracic segment appears to be limited in front by a definite 
groove, which would thus separate the cephalic and thoracic regions 
(Lister, 1909, p. 436, footnote). 
