-j^QQg CRUSTACEA. 



This species has most of the characters mentioned for M. Edwards's 

 Phorms Raynaudii: but, he observes, that the antennae are " un peu 

 renflees vers le milieu;" while, in this species, the basal portion is 

 stout ellipsoidal. Moreover, he states, that the second thoracic ring 

 is very much developed, and the fifth pair of legs is shorter than the 

 sixth. 



Family TYPHID^. 



The peculiar character of the outer antennae of the Typhidas— their 

 being folded up and concealed beneath the head or thorax — is consi- 

 dered a character of higher value than the flexing of the abdomen 

 against the venter, which is observed in some of the species, although 

 the latter produces striking peculiarities in the form and habits of 

 the species. The antennae are organs high in rank, from their con- 

 nexion with the senses ; and hence, a peculiarity of structure in them, 

 prevailing through a group of species, is entitled to prominent consi- 

 deration. On the contrary, this power of flexing the abdomen to the 

 venter is deemed of small importance among the Oniscidae and Sphe- 

 romidae, and does not even authorize in the latter case a subfamily 

 division. The transitions, moreover, among the species which have 

 the peculiarity alluded to and those without it, are very gradual. 

 The species are, therefore, here retained in a single family, although 

 the extreme forms are very diverse. 



The subfamilies and genera of Typhidae, are as follows : 



Subfam. 1. TYPHIN^E.— Abdomen in ventrem se flectens. 



G-. 1. DiTHYRUS, Dana.— Pedes 5ti 6tique articulo lmo late lamellati, articulis 

 reliquis omnino obsoletis. Antennas 2das breves, sub capite celatas, non reph- 

 catre, articulo lmo longiore quam 2dus. 



G. 2. Typhis, Risso.— Pedes 5ti 6tique articulo lmo late lamellati, articulis reli- 

 quis paulo abbreviatis. Antennas 2dae biplicatae, articulo lmo longiore quam 



2dus. ■ • v 



G. 8. Thyropus, Dana.— Pedes 5ti 6tique articulo lmo late lamellati, articulis 

 reliquis paulo abbreviatis. Antennas 2dae 4-5-plicatae, sub thoracis latere celatas, 

 articulo lmo multo breviore quam 2du&. 



