150 



The antenna! scale, when present, is of small or medium size, and never 

 wholly conceals the antennal peduncle. 



The external maxillipeds are almost always pediform and are always much 

 shorter than the 1st pair of thoracic legs. 



All five pairs of thoracic legs are almost always strongly developed : a 

 variable number of them — sometimes all, sometimes the 1st alone, or the first 2, 

 or the first 3, sometimes the last alone, sometimes none at all — are chelate, and 

 the 1st pair are usually much longer and stouter than any of the others. 



The appendages of the 1st abdominal somite, when present, are uniramous 

 and are often modified in the male for copulation. 



The genital openings of the male are pierced in the coxopodites of the 

 5th pair of thoracic legs. 



The Astacides may be divided into two groups, namely 



(1) The Astaeidea proper, in which all the segments of the thoracic sternum 

 are usually but not always firmly united, and in which the abdominal terga overlap 

 one another, and 



(2) the Thalassinidea, in which the last segment of the thoracic sternum is 

 independent, and the abdominal terga do not overlap one another or overlap 

 very slightly. 



Synopsis of the families of Macrura Astacides of the Indian Benthos. 



I. All the thoracic sterna are firmly united together : the abdominal terga 

 overlap one another, aud the abdominal pleura behind the 1st are well 

 developed : — 



1. Carapace subcyliudrical, ending in a long strong rostrum ; its 



anterolateral inflexions are not fused with the epistome, and its 

 postero-lateial angles, though they lie beneath the projecting 

 angles of the 1st abdominal tergum, are not firmly held by 

 any pegs or processes. In the 2nd maxilla? and 1st maxilli- 

 peds the manducant functions are not less important than 

 the respiratory. Thoracic sternum narrow. [The antennal 

 peduncle consists of five movable joints, and the flngellum is 

 a long lash. All the maxillipeds have flagelliform exopodites. 

 The first 3 pairs of thoracic legs are chelate and the 1st pair 

 much enlarged. The telson is quadrangular or truncated. 

 The 1st abdominal somite has a pair of uniramous appen- 

 dages]. Nephropsidea ... ... ... ... NBPHROPSID*. 



2. Carapace either subcyliudrical (rarely globose) or depressed ; 



anteio-laterally it is fnsed with the epistome, and its postero- 

 lateral angles are firmly held by special pegs or processes of 

 the 1st abdominal somite : the rostrum is either absent or 

 represented by a mere spine. In the 2nd maxilla? and 1st 



