V AMPHIPODA—CREVETTINA 13 
N 
cluding a vast assemblage of very similar animals, of which the 
common Gammarus and Orchestia may serve as examples; (11.) 
the Laemodipoda or Caprellids, and (iu.) the Hyperina. 
We cannot do more than touch on the organisation of these 
sub-orders. 
Sub-Order 1. Crevettina. 
In this sub-order only one thoracic segment is fused with the 
head ; the basal joints of the thoracic limbs are expanded to form 
broad lateral plates, and the abdomen is well developed, with six 
pairs of pleopods, the last three pairs being always turned back- 
wards, and stiffened to act as uropods, 
This group has numerous fresh-water representatives, ¢.7. 
Gammarus of several species, the blind well-shrimp Niphargus, and 
the 8S. American Hyalella; but the vast majority cf the species 
are marine, and are found especially in the littoral zone wherever 
the rocks are covered with a rich growth of algae, Polyzoa, ete. 
The Talitridae or “Sand-hoppers” have deserted the waters and 
live entirely in the sand and under rocks on the shore, and one 
common European species, Orchestia gammarellus, penetrates far 
inland, and may be found in gardens where the soil is moist 
many miles from the sea. 
The Rev. T. R. R. Stebbing, in his standard work! on this 
group, recognises forty-one families, and more than 1000 species, 
so that we can only mention a few of the families, many of 
which, indeed, differ from one another in small characters. 
Fam. Lysianassidae.—The first joint of the first antenna is 
short, with an accessory flagellum. Mandible with a palp, and 
with an almost smooth cutting edge. The third joint of the 
second gnathopod is elongated. This family is entirely marine, 
comprising forty-eight genera, with species distributed in all seas. 
One genus, Psewdalibrotus, inhabits the brackish water of the 
Caspian Sea. Lysianassa has several common British and 
Mediterranean species. 
Fam. Haustoriidae.— The members of this family are 
specially adapted for burrowing, the joints of the hinder thoracic 
limbs being expanded, and furnished with spines for digging. 
Some of the species are common on the British coasts, eg. 
Haustorius arenarius. Pontoporeia has an interesting distribu- 
' “as Tierreich,” 21, Amphipoda Gammaridea, 1906. 
