Yol. 52.] ANNIVERSARY ADDRESS OF THE PRESIDENT. Cxiii 



regions large. The epistome is generally large, and the buccal region 

 quadrate, with a straight anterior margin. 



In long-bodied Crustacea the nervous system is divided into 

 two parallel chords, with separate ganglia for each segment. In 

 the Spider-Crabs the nervous system attains a high degree of 

 concentration, there being only a thoracic and a cephalic ganglion, 

 instead of about 15 separate centres, as in Homarus. Notwith- 

 standing this high degree of cephalization, they do not display any 

 great activity, but are generally of sluggish and slow-moving habits, 

 their intelligence being principally directed to the arts of disguise 

 and concealment in which they certainly display mnch ingenuity, 

 especially in planting their backs and legs with seaweeds, corallines, 

 Alcyonia, and the like, which they have been observed to change, 

 from time to time, the better to suit the colours of their altered 

 habitats. 



This is undoubtedly one of the oldest tribes represented in 

 geological time, being met with as far back as the Forest Marble 

 (Great Oolite) of Wiltshire, and it disputes with the Dromiacea the 

 ancestorship of all the short-tailed Podophthalma. 



As before remarked, the earliest known crab is the Palceinachus 

 longipes, H. Woodw., Forest Marble, Great Oolite, Malmesbury, 

 Wiltshire. This is followed by Lissiopsis transiens, Fr., from the 

 Chalk of Bohemia. 



Lambrus nummuliticus, Periacantlius liorridus, and Micromaja 

 tuberculata, of Bittner, are all from the Eocene of Yicentino and 

 other districts of Northern Italy. 



Micromithrax holsatica, from the Miocene of Holstein, a species of 

 Maija from the Miocene of Malta and another from the Coralline 

 Crag of Suffolk, complete the list of the sharp-nosed crabs. 



Cyclometopa. — The crabs which are placed in the tribe of the 

 Cyclometopa have the carapace arched in front and often broader 

 than long ; more rarely it is quadrate, or suborbicular, but in none 

 of the members of this division is the carapace rostrate. It includes 

 the Cancridea, Cyclinea, and Thelphusinea. [The Corystinea I 

 would prefer to place with the Oxystomata.] Here is located that 

 most ancient and astronomical genus — Cancer, with Xantko, Ozius f 

 Trapezia, Carcinus, Portunus, Polybius, Podophthalmus, Thelphusa, 

 and many more well-known forms, several being largely eaten 

 by mankind. Members of the Portunidae occur in the Eocene, and 

 of the Cancridae as far back as Cretaceous times. 



The Cyclometopa (circular-fronted crabs) of the division Can- 



