REPORT ON THE ANOMURA. 49 



mentioned habit. Many of the species live in a state of commensalism with an Actinia 

 which adheres to the exterior of the shell, and in some cases at least the two are 

 invariably found together. 



The Pagurodea are divisible into two branches according to the structure of the gills, 

 whether of the normal phyllobranchiate type as in other Auomura, or of the tricho- 

 branchiate type as in many Macrura. These may be termed Laminibranchiata and 

 Fibribranchiata respectively. 



LAMINIBRANCHIATA. 



Family I. C CE N o b i T i d .e. 



Cenohitidx, Dana, U.S. Explor. Exped., vol. xiii.. Crust., part i. p. 432, 1852. 

 „ Stimpson, Proc. Acad. Nat. Sci. Philad., p. 70, 1858. 



„ Haswell, Catal. Austral. Crust., p. 159, 1882. 



Antennular peduncle greatly elongated, the first joint deflexed and as long as or 

 exceeding the eye-stalks, the second and third joints narrow and cylindi-ical ; one of the 

 flagella enlarged. Antennal peduncle compressed, the terminal joint long. Species 

 subterrestrial. 



This family includes the genera Birgus and Coenohita, the species of which are 

 confined to tropical and subtropical regions. Their afiinity with Lithodes, which was 

 noticed by Milne-Edwards, though he did not accordingly group them together, is well 

 seen in the form of the abdomen. 



Genus Birgus, Leach. 



Birffiis, Leach, Trans. Linn. Soc. Lond., vol. xi. p. .337, 1815. 

 ,, Desmarest, Consid. sur les Crust., p. 180, 1825. 

 ,, Milne-Edwards, Hist. Nat. des Crust., t. ii. p. 244, 1837. 



De Haan, Crust. Japon., p. 20.3, 1850. 

 „ Dana, U.S. Explor. Exped., vol. xiii.. Crust., part i. p. 435, 1852. 

 ,, Stimpson, Proc. Acad. Nat. Sci. PhQad., p. 70, 1858. 



Carapace broadly ovate, with a prominent rostrum in front. Ocular peduncles 

 cylindrical. Abdomen not twisted, broad, the second, third, fourth and fifth segments 

 each with a large, corneo-calcareous, overlapping tergal plate, which occupies the whole 

 width of the segment, and with smaller lateral plates. Under surface of the abdomen 

 membranous, with a plate situated posteriorly, which represents the sixth segment and 

 is provided with a rudimentary appendage on each side ; attached to this is a telson of 

 small size. Eespiratory chambers spacious, containing fourteen gills on each side, and in 

 addition vascular pulmonary outgrowths. 



(ZOOL. CHALL. EXP. PART LXIS. 1887.) , ZzZ 7 



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