GEOGRAPHICAL DISTRIBUTION OF CRUSTACEA. 1515 



large size, and the adult Homari and Palinuri are not exceeded in 

 weight by any other Macroura. 



The Thalassinidea, which belong almost exclusively to the tempe- 

 rate regions are smallest in the warmer part of the Temperate zone, 

 and larger in the middle and colder part. A Puget Sound species 

 (subfrigid region) of Callianassa (C. gigas) is at least four and a half 

 inches long, the G. uncinata of Chili, five inches, and the Thdlassina 

 scorjpionides of Chili, six inches. The facts respecting this subtribe, 

 added to those mentioned above, strengthen much the conclusion, that 

 the cold-water genera have the largest species ; for all the species are 

 over an inch and a half in length. 



III. ANOMOBRANCHIATA. 



XXIV. The Mysidea, to which the Penaeidea are related, are, to a 

 considerable extent, cold-water species, although many are found also 

 in the tropics. There are among them twenty torrid species and 

 seventeen extra-torrid species. 



In the Squilloidea we have an example of an inferior grade in a 

 large lax body, with a small head and long abdomen; and they 

 remind us of overgrown larval forms, or species vegetatively enlarged 

 beyond the normal or most efficient size. In this particular they 

 have some analogies with the earlier forms of life. They are found 

 mostly within the tropics. Twenty-four of the Squillidaa are Torrid 

 zone species, and only seven pertain exclusively to the Temperate 

 zone. Of the Erichthidae, twenty-one out of twenty-two species are 

 reported from the Torrid zone. The Amphionidea, a related group, 

 include seventeen Torrid zone species and two of the Temperate zone. 



