PODOPHTHALMIA. 51 



and Pagurus. In these genera, the eyes are anterior to the first 

 antennae, even pertaining to a separate annulus ; and the second 

 antennse are still more posterior, and usually exterior to the eyes. 

 Thus the concentration and close conjunction of the organs of the 

 senses, so characteristic of the typical Maia, gradually fades, and 

 these organs instead of being combined, begin to take on an arrange- 

 ment in series like the posterior members of the body. The abdomen 

 is also largely developed, and in Pagurus a pair of appendages to the 

 penult segment unites with the last segment in forming a caudal ter- 

 mination to the body, like that of the Macroura. The posterior 

 thoracic legs are short ; and other characters show the grade of the 

 species to be but little removed from the true Macroural type. 



Descending still lower, we come into the range of the Macroura. 

 The family which appears to represent the Paguri, is the Thalassina 

 group. This is seen in the form and markings of the cephalothorax; 

 the characters of several of the legs; the first and third pairs of 

 maxillipeds; and the outer antennae mostly without an appendicular 

 plate. The abdomen has the true Macroural character, being fully 

 elongated, and furnished with a range of appendages below, in 

 both sexes. On a still lower level, we find this type again repre- 

 sented in the Squillidae, to which group, certain of the Thalassi- 

 nidea show an approximation. The Squillidse, without thoracic 

 branchiae, are among the lowest of Crustacea with pedunculate eyes, 

 and belong to the group Anomobrancliiata. 



We have thus followed the Maioid type in its degradations to the 

 Macroura, or even below this level. We may pursue the same course, 

 though not in all cases to the same extent, with the other' grand divi- 

 sions. 



It was seen that the Maioidean series passes down from the Parthe- 

 nopinea, the lower type of the division. An obvious series direct 

 from the Cancroidea, passes through the Corystoidea, which have a 

 relation to the Cancroids somewhat similar to that which the Par- 

 thenopinea have to the Maioids, excepting a wider separation. The 

 group into which the Corystoidea leads is the Hippidea. The form of 

 the narrower species approaches Hippa ; the antennae are very similar : 

 the legs in the swimming species show an approach to this group ; 

 and in general aspect, also, there is much resemblance. But in 

 the Hippidea, the abdomen is much elongated and has appendages 

 either side of the last segment; the last thoracic legs are short, and 

 the species present the various other characteristics which widely 



