Manchester Memoirs, Vol. Ixv. (192 1), No. 11 3 



not preserved. They were taken from a large robustly- 

 branched coral of the genus Acropora (= Madrepora) which 

 was growing at a depth of one or two fathoms in the harbour 

 of Pago Pago, American Samoa. Hapalocarcinus has been 

 taken on various corals, but it is not yet recorded from 

 Acropora. Details of the structure and mode of formation of 

 the gall are not available, but it was unlike that of Hapalo- 

 carcinus. though the prawns were well enclosed. It did not 

 project, but was hollowed into the coral. 



The body of the female has the heavy, clumsy, and 

 simplified aspect which is commonly presented by members 

 of an active group of animals that have taken to a sedentary 

 life, and are therefore able to further reproduction by sacrificing 

 that elegance which is the result of adaptation to acute 

 perception and swift movement. In this respect, and indeed 

 to some extent in the main outlines of its build, it resembles 

 Hapalocarcinus, though, since its anatomy is that of a prawn, 

 the details that make up its habit of body are naturally 

 different from those of the crab, and recall rather the extreme 

 members of the series of similar adaptations which is found in 

 the Pontoniine prawns. 3 Among these, indeed, it shows a 

 considerable likeness to Conchodytes, which lives within the 

 shells of bivalve molluscs, though this prawn is less degenerate 

 than Paratypton. The back is broad, but its breadth is largely 

 due to spreading branchiostegites and abdominal pleura. 

 Between the branchiostegites the cephalothorax is rather 

 compressed and narrows gentlv forwards. It is altogether 

 without rostrum, the front being almost straight, and, in 

 Balss' specimen, though not in mine, exposing in a dorsal 

 view the convex middle region of the eye segment. The 

 anterior edge of the branchiostegite projects forward beyond 

 the median region of the carapace and bears no spines or 

 angles whatever. The abdominal pleura, particularly the first 

 four, are very large and, arching, enclose on the under side 

 of the body a great brood-pouch in which lie the abdominal 

 limbs. Trie last pair of limbs, with the telson, complete the 

 pouch wall. The abdominal segments are altogether without 

 spines or angles save that the hinder angles of the sixth 

 segment project sharply. The cuticle of the body is every- 

 where very thin and perfectly smooth. 



3. A group of prawns treated by some authors as a sub-family of the 

 Paleemonidae, and by others as a separate but closely related family. Many of 

 its members are commensal, or at least associated, with sessile or sub-sessile 

 organisms. 



