276 S. I. Si/nth — Amjjhipodus (jenera, 



obstruction. Wliile thus held last, fully lialf the body is ot'ten 

 protruded from the tube. In turning about within the tube, the 

 terminal segments of the pleon are thrust forward beneath the an- 

 terior segments and the peneon pulled back over them, and tlien the 

 peraeon is folded back upon itself in the same way, but the anteu- 

 nula?, antennjB and head are never first bent beneath the perason. 

 The structure of the telson, second and third uropods, and of a part of 

 the pera30pods is well adapted to the performing of this evolution ; the 

 hooks of the second and third uropods and of the telson holding the 

 tail fast to the side of the tube, while the third, fourth and fifth 

 perajopods, holding on with tiieir opposing hooked tips, pull the 

 posterior part of the perreon back over tlie pleon, and then the first 

 gnathopods help to complete the evolution. 



The tubes are usually kept quite free from foreign growtlis, but 

 among the specimens taken in 1874, there are two individuals in 

 tubes to which are attached the egg capsules of Tritia trivittata. 



I Avas not able to discover how the diameter of the tube is en- 

 larged to accommodate the growing animal, but it is probably 

 accomplished by building on a larger portion at one end and pulling 

 to pieces the other end until the whole tube is reconstructed. 



As the preceding description shows, this type species of the genus 

 Cerapiis is generically distinct from the species referred to that 

 genus in recent works, and for which Milne-Edwards' genus Eric- 

 thonius may properly be retained as explained further on. Say's 

 species is apparently not congeneric with any described species and 

 the genus cannot properly be placed in any of the numerous sub- 

 families defined by Boeck, though it is probably most nearly allied 

 to his Podocerinae. I therefore propose the following new sub- 

 family to be placed next Podocerinae. 



Cerapin.e. 



The single known genus differs from the Podercerinae and allied 

 groups in the following characters. There are only three pairs of 

 branchial lamellas, wdiich are borne on the third, fourth and fifth 

 segments of the peraeon, and only three pairs of ovigerous lamellae, 

 which are borne on the second, third and fourth segments. The 

 second and third pleopods are much smaller than the first, and their 

 inner lamellae are rudimentary or very small. The second and third 

 uropods are uniramus and nearly alike, the distal segment in each 

 being short and terminating in a hooked point. 



