22 PHRONIMID^E. 



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. 



