22 PHRONIMIDA. 
six joints in each, but which of the joints is missing 
is difficult to determine. Observing, however, that the 
finger in the first two pairs is reduced to a rudimentary 
condition, and knowing the tendency in this division for 
the wrist to assist in forming the prehensile condition of 
the organ, we presume that the last joint is either wanting 
or fused with the preceding. In one instance we have ob- 
served a minute dactylos at the extremity of the second 
pair of pereiopoda, but so minute that it was not ap- 
preciable to less than 60 diameter magnifying power, and 
it is most probable that it is absent from being generally 
worn away. (We have a parallel instance in the allied 
subfamily Phrosinides. In the genus Phrosina the num- 
ber of joints is six, whereas in Primno it is seven. Five 
joints of the legs resemble each other in the two genera, 
but in Primno the finger is added to the extremity.) 
The fourth pair of legs are very perfectly chelate. The 
caudal appendages are biramose, the rami being short and 
spear-shaped. The middle tail-piece is small, and slightly 
emarginate at its extremity. The animals of this genus 
are generally to be met with in tropical and subtropical 
waters and the Mediterranean. The few specimens which 
we know to have been met with in the Temperate Zone, 
have been probably borne thither by various oceanic 
currents. 
