The second pair of mesosomatic appendages in Scorpio are known as the " pectens."
The " pectens " have become more firmly chitinized and probably somewhat altered in shape as compared with their condition in the aquatic ancestral scorpions.
Palamnaeus indus, de Geer, to show the arrangement of the coxae of the limbs, the sternal elements, genital plate and pectens.
In Limulus small entosternites are found in each somite of the appendage-bearing mesosoma, and we find in Scorpio, in the only somite of the mesosoma which has a welldeveloped pair of appendages, that of the pectens, a small entosternite with ten pairs of muscles inserted into it.
The meeting of the coxae of all the prosomatic limbs in front of the pentagonal sternum; the space for a genital operculum; the pair of pectens, and the absence of any evidence of pulmonary stigmata are noticeable in this specimen.