Hapalocarcinus, the Gall-forming Crab, etc. 67 



THE AFFINITIES OF THE HAPALOCARCINIOE. 

 On this subject Caiman writes as follows: 



"While the characters of Hapalocarcinus, as now described, show clearly 

 that it must stand alongside Crypt ochirus, they give little help towards settling 

 the place of the two genera in the system. The position of the female genital 

 apertures shoAvs that they must be placed among the true Brachyura, although 

 there are some curious resemblances to individual genera of the Anomura. 

 Thus the endopod of the third maxillipeds resembles somewhat that of 

 Porcettana, while the rudimentary exopod suggests a comparison with the 

 Hippidea. The number and uniramous condition of the abdominal append- 

 ages also agree, except for the absence of the sixth pair, with the last-named 

 group. These resemblances, however, are balanced by numerous important 

 differences, so that even were we to set aside the evidence of the genital open- 

 ings it would be impossible to place the genera in any of the groups of Anomura. 

 On the other hand, the characters of the third maxillipeds and of the abdominal 

 appendages and the greatly enlarged buccal area are unlike anything found 

 among the Brachyura. The resemblance to the Pinnotheridse appears to be 

 quite superficial." 



My own opinion coincides almost exactly with that of Caiman, but I 

 am inclined to lay even less stress on the resemblances to the Anomura. 

 The characters of the male are typically Brachyuran. The likeness 

 between the third maxillipeds of Porcettana and Hapalocarcinus is 

 due to a similar mode of feeding. I have dealt at length with two of the 

 divergences from the Brachyuran type mentioned by Caiman; and the 

 third, the character of the abdominal appendages, is more nearly paral- 

 leled by Pinnotheres amongst the Brachyura than by the Hippidea, as 

 Caiman suggests. But in spite of this fact I thoroughly agree that 

 there is no near relationship between Hapalocarcinus and Pinnotheres. 

 Caiman says further with regard to this point : 



"In describing Hapalocarcinus, Stimpson noted its resemblance to Pinno- 

 theres in the large size of the abdomen and the softness of the integument, 

 and he stated that its systematic position was probably between Pinno- 

 theres and Hymenosoma. Apart from the two points mentioned, there seems 

 to be little in the characteristics of the species as now described to suggest 

 affinity with the Pinnotheridse, while the third maxillipeds are widely different 

 in type from anything found in that group." 



In Hapalocarcinus 9 there are three pairs of abdominal appendages, 

 while Pinnotheres 9 possesses the normal number, four. There is, how- 

 ever, in both a tendency to a complete suppression of the exopod, a 

 tendency not exhibited in other Brachyura, so far as I know. 



The following statement of the appendages forms the basis for a 

 more exact comparison: 



