REPORT ON THE CRUSTACEA MACRURA. ix 



The teeth also that are placed upon the frontal margin of the carapace are probably 

 less offensive than protective, since they generally are situated at points where muscular 

 attachment is required, and the strength of the integumental tissue is by their presence 

 increased. 



Although the carapace has the capacity of being elevated posteriorly at the will of 

 the animal, it is nevertheless generally kept in position by strong points of resistance, and 

 these vary in form, position, and character in different families and perhaps in genera 

 also. In Palinurus they exist as large, flat, button-shaped tubercles on each side of the 

 pereion and are inserted into hollow cavities on the under surface of the carapace, and 

 the power of retention is very great. To such a tubercle I have applied the name 

 pereicleis, since it bolts the carapace to the pereion (PI. XII. fig. 1, Palinosytus 1 ; fig. 2, 

 Panulirus). 



In other genera, such as Thaumastocheles (PI. VI.), Ibaccus (PI. VIII.), and Pentacheles 

 (PI. XVI. fig. 4), there is a process or tubercle on the pleon that overlaps the carapace, and 

 keeps it in position. This I have named the pleocleis. In some few instances, as in 

 Willemcesia, the tubercle originates from the posterior margin of the carapace and lodges 

 in a groove or hollow in the surface of the first somite of the pleon ; this I have named 

 the peltocleis. But in many genera the carapace is produced posteriorly on each side to a 

 considerable extent, and while overlapping the first somite of the pleon is itself over- 

 laid by the anteriorly projecting wings of the second somite. 



The Branchise. — The great value of this power of securing the carapace is that 

 it gives protection to the branchiae which are placed beneath it. 



Where the carapace does not exist, the branchiae are of a more simple character and 

 are generally pendent from the leg, as in the Amphipoda, or attached to other parts of 

 the animal, as in the Squillidae and Isopoda, or are absent altogether as in Lucifer. But 

 in the well-developed forms of Macrura the branchiae assume a higher character than 

 mere appendages of the legs. 



It is true that one pair (the podobranchise) belong to the first or coxal joint of the 

 legs, and these are developed largely and most constantly in the normal group of the 

 Trichobranchiate division, being absent only in two genera, and in some of the normal 

 forms of the Dendrobranchiata, as in the genera Benthesicymus, Aristeus, and their near 

 congeners ; but they are absent in Penseus, Sicyonia, and Sergestes, and rudimentary in 

 Haliporus. 



In the Phyllobranchiate division the podobranchial plume is invariably absent from 

 all the pereiopoda, but it is present — except in only a few genera, such as Nika, Crangon, 

 and Glyphocrangon — on the first pair of gnathopoda, and in the fresh-water genus Atya 



1 A. Milne-Edwards having employed Palinmtus for the name of a new Seyllarid, I have changed the name of my 

 genus from Palinostns to Palinotytus. 



(ZOOL. CHALL. EXP. —PART LII. 1888.) Fff & 



