12 ON A PYCJS'OGONID OF THE GENUS HALOSOMA, 



Beach, California. It is very closely related to both. 

 Fhoxichil id mm axid Anoplodactylus, more closely to the 

 latter than to the former. Halosoma differs from these 

 genera, as Cble shows, in its greater concentration pro- 

 ducing a stO'uter trunk and closely approximated lateral 

 processes; further, in the moderate development of the 

 neck it is intermediate between the two genera mentioned.. 

 In his definition of the genus. Cole describes the second 

 tarsal joint (propodus) as possessing a well expanded spin- 

 ous heel and "a thin chitinous knife-like ridge along the 

 sole," a well developed claw and minute auxiliary claws. 



The position of Cole's genus has been considered by 

 •Loman (4), who comes to the conclusion that Halosoma 

 should be regarded as a subgenus of Anojjlod actylus . This 

 author gives a list of a number of Pycnogonida already 

 described in literature which in his opinion should be 

 included under Halosoma, viz. : — 



Pallene laioya, Bohm, 1879. 



Phoxicliilidmm exiguum, DohrUj 1881. 



Halosoma virid intestinal is, Cole, 1904. 



Anoijlodactyl'us anarthrus, Loman, 1908. 

 AVithout modifying in any way Cole's original definition 

 of the genus, Loman shows that all the above enumerated 

 species agree in the following points:- — 



(a) Arrangement of the special spine® of the legs (a. 



single spine at the distal end of the feimur and 

 of the 1st tibia,, and one placed some little dis- 

 tance from the distal end of the 2nd tibia). 



(b) Structure -of the tarsus and propodus and their 



relationship to one another and to the large claw 

 which is able to close up against the propodus likei 

 the blade of a penknife. 

 I am inclined, after consideration, to follow Cole in mak- 

 ing Halosoma a separate genus. 



The points in which Halosoma differs from Anoplo- 

 dactylus — ^the particularly small size, the crowded nature 

 of the crurigers (5), the tendency of the trunk segments 

 towards coalescence, the feeble development of the neck, the- 

 particular arrangement of the spines on tne legs, and the 

 structure of the tarsus and propodus (all of which points 

 are mientioned by Lo-man) — are sufficient, in my opinio'n, 

 to' characterisie Halosoma as a distinct genus. 



(A) 1912 Loman. Bull, de I'Inst. Oceanog, No, 238, p. 6. 



(5) Such expressions as "lateral processes," "lateral prolonga- 

 tions," etc., are to be regarded as descriptions rather than scientific- 

 terms, and I therefore suggest the use of the term "cruriger" to de- 

 note in a Pycnogonid the hollow process of the body wall to which 

 the ambulatory leg is attached. 



