NO. 4 HARTMAN : POLYCHAETOUS ANNELIDS 437 



defined in lateral view; the beak consists of a larger basal fang with a 

 smaller secondary fang above it; this is surmounted by a transverse ridge 

 terminating in 3 short denticles (pi. 55, fig. 3). The hood is voluminous 

 and has a large aperture; its margin is only slightly toothed. The 

 pygidium is a large dorsal aperture at the end of the body; it lacks 

 appendages. 



D. platyceps is characterized in having branchiae that are dendriti- 

 cally branched and emerge from a pore above abdominal neuropodia; 

 they are continued through a long region, present already from the 

 thirteenth and continued nearly to the end of abdominal segments. The 

 thoracic epithelium is only slightly areolated; the surface epithelium 

 throughout appears nearly smooth under low magnification. Lateral 

 organs are present on all segments. Nephridial apertures number about 

 15 pairs and are present in posterior thoracic and anterior abdominal seg- 

 ments. Abdominal uncinal ridges are well separated from one another 

 throughout. Hooded hooks have a beak with primary and secondary 

 fangs crowned by a crest of 3 short denticles on a transverse ridge. D. 

 platyceps is separable from other species of the genus as indicated in the 

 key above. 



The single collection on which this species is based was made by Mr. 

 Steve A. Glassell in May 1941, to whom thanks are hereby extended. 



Holotype.—ARY no. 122. 



Type locality. — Sonora, Gulf of California, Mexico ; intertidal. 



Distribution. — Gulf of California, Mexico. 



Genus LEIOGAPITELLA, new genus 

 Type L. glabra, new species 



The thorax and abdomen are not distinctly separable in external view. 

 The thorax consists of 14 or 15 segments, the peristomium or first seg- 

 ment is achaetous and apodous. The second segment has notopodia only ; 

 the third to fourteenth segments are provided with fascicles of pointed 

 setae in both notopodia and neuropodia ; the fifteenth segment has pointed 

 setae dorsally and long-handled hooks ventrally; thereafter at least to 

 the fifteenth segment parapodia have only long-handled hooks in both 

 rami of parapodia or the superior part of the fifteenth notopodium may 

 continue to have a few pointed setae accompanied by a ridge of hooks. 

 Lateral organs are present on all known segments, located between noto- 

 podia and neuropodia; on the thorax they are retractile, on the abdomen 



