PODOPHTHA LMIA. 



55 



Fig. 65. — Phyllosoma, glass crab, the larva of Palmurus, natural size. 



feet monodactyle, that is, not ending with a pincer, but in their development they pre- 

 sent marked differences, the young forming the "glass crabs," which formerly, under 

 the name Phyllosoma, were 

 regarded as adults. These 

 larvae are flattened, hardly 

 thicker than a sheet of 

 paper, and in life are per- 

 fectly transparent, present- 

 ing not the slightest resem- 

 blance to the parents. The 

 two families, Sctllaeid^ 

 and Palinueid^, are found 

 in tropical seas, and are 

 among the largest Crustacea. 

 All of the feet, except the 

 posterior pair in the female 

 Scyllaridffi, are monodactyle, 

 while the antennal scale is 

 always lacking. The Palin- 

 uridse are nearly cylindrical, 

 while the Scyllaridse are 

 .greatly flattened, the sides of the body being very thin. Both families are repre- 

 sented in our warmer waters by the genera Palinurus and Panulirus, Scyllarus, 

 Ibacus, Evibacus, and Arctus. 



The THALASSINIDEA, represented in our waters by several genera, are a bur- 

 rowing group, the individuals of which, except from a scientific standpoint, are of but 

 slight importance. While in the majority of forms the respiratory apparatus is of the 

 normal character, it is said that in Callianidea (of which one species occurs in the 

 West Indies, the other extending from our west coast through all the eastern seas) 

 and in CaUianisea the abdominal feet also bear gills, thus presenting a resemblance to 

 the Stomatopoda, to be described further on. 



The GALATHEIDEA present us with a feature which we shall notice in connec- 

 tion with the Schizosomi, that the hinder pair of thoracic feet are cariied bent up 

 under the carapax, and in both groups, as in the Paguridea, the last thoracic segment 

 is not immovably united to the rest, a feature which also occurs in the genus Astacus. 

 Grimothea is a pelagic form which occurs swimming at the surface in the Pacific 

 Ocean, sometimes appearing on the Californian shores. uEglea is a fresh-water genus 

 (the only one of the Anomura), and the single species occurs in the streams of Chili 

 and Peru. 



The last division of the Macrura which we have to consider is the PAGURIDEA, 

 or hermit crabs. In these forms, with the exception of Pirgus, the abdomen is 

 always soft, the usual salts of lime not being deposited, and hence the animal inserts 

 this defenceless portion of his body in the empty shell of some univalve mollusc. 

 With this external protection there is usually an obsolescence of some of the abdominal 

 feet, while the spiral character of the shell has caused the abdomen to become coiled 

 , in a similar manner. The posterior pair of abdominal feet are modified so as to form 

 a hook, by means of which the crab holds himself into his house. 



Many amusing accounts have been given of the habits of the hermit crabs, and we 



