NO. 1 HARTMAN : POLYCHAETOUS ANNELIDS 37 



Halosydna, species A 

 Plate 4, Figs. 51-55 



Collection. — 719-37. One specimen. 



General color pale flesh, but under low magnification the elytra are 

 seen to have dispersed reticulated rust-colored blotches, that are darkest 

 and most concentrated in anteriormost elytra, and more or less limited 

 to an area over the hilum in posterior elytra. The dorsal cirri have a 

 broad dark band subterminally. Setae and acicula are pale amber; palpi 

 and prostomial antennae rust-colored. 



The unique specimen is coiled, but measures about 27 mm long w^hen 

 stretched out. It includes 33 setigerous segments. The prostomium is 

 lepidonotoid, with a shallow median sulcus throughout, the 4 subequal 

 black eyes located at the sides and posterior margin of the prostomium. 



There are 18 pairs of elytrophores. The elytra are more or less 

 loosely attached, but most are still present. They completely cover the 

 dorsum. The marginal fringe is limited to the external margin. The 

 surface is ornamented with some large, button-like, soft papillae (pi. 4, 

 fig. 54) most numerous on anterior elytra, but some are present through- 

 out. In addition, the surface is diffusely covered with microtubercles 

 each of which has a small horny projection. The rust-colored blotches, 

 under high magnification, are seen to consist of numerous polygonal 

 areas (pi. 4, fig. 55). 



Parapodia subbiramous, the notopodium obsolete, inserted on the 

 dorsal side of the neuropodium. It is provided with a small fascicle of 

 about 12 to 15 short, notopodial setae, their free portions less than half 

 as long as the free ends of the neuropodial setae. They include shorter, 

 curved, denticulated, superior setae (pi. 4, fig. 53) and longer, slender, 

 serrulated inferior setae (pi. 4, fig. 51). Neuropodia are robust, taper- 

 ing slightly to a truncate acicular lobe from which the yellow aciculum 

 projects a short distance. The neuropodial setae emerge from the lobe 

 in about 2 trim vertical rows, and include about 25 setae in a median 

 parapodium. They are minutely bifid at the tip (pi. 4, fig. 52), the 

 accessory tooth nearly parallel to the main shaft. The transverse rows 

 of serrations increase in size distally. 



The elytral and setigerous structures of this specimen do not com- 

 pare favorably with those of any known species of Halosydna. Further- 

 more, it originates from a locality (Consag Rock, upper end of the 

 Gulf of California) which has not been biologically investigated here- 

 tofore for its chaetopod fauna. 



Distribution. — Upper end of Gulf of California, Mexico. In 20-25 fms. 



