310 U.S. NATIONAL MUSEUM BULLETEST 227 



Trochochaeta multisetosa (Oersted, 1843) 



Figures 82, 83,a-g 



Disoma muUisetosum Oersted, 1843, p. 41; 1844, p. 107, pi. 2, figs. 1-12 (anterior 

 fragment) .—Eliason, 1920, p. 59.— Timlin, 1921, p. 9, figs. 7-17.— Wesenberg- 

 Lund, 1950a, p. 31, pi. 7, figs. 31-32; 1951, p. 73.— Uschakov, 1955, p. 284, 

 figs. 101-102.— Hannerz, 1956, p. 141, figs. 51-52. 



Trochochaeta sarsi Levinsen, 1883, p. 129, pi. 2, figs. 6-7 (posterior fragment). 



Thaumastoma singulare Webster and Benedict, 1884, p. 737, pi. 7, figs. 85-94 

 (anterior fragment) . 



Nevaya whiteavesi Mcintosh, 1911, p. 149, pi. 5, fig. l,a-h. 



Spionid larva D. Thorson, 1946, p. 97, fig. 50,a-d (see Hannerz, 1956, p. 146). 



Disoma franciscanum Hartman, 1947a, p. 16, figs. 1-3. 



Remarks. — Thaumastoma singulare was described from a single 

 incomplete and rather mutilated specimen, the family of which was 

 not determined. Mesnil (1897), using the original description and 

 figures, referred it to Disoma multisetosum. Because of discrepancies 

 in the descriptions, Hartman (1947a) thought it advisable to regard 

 Thaumastoma singulare as an indeterminable genus and species. On 

 the basis of a study of the slides of the typo specimen in the U.S. Na- 

 tional Museum, I have concluded that Mesnil was correct in referring 

 it to Disoma multisetosum. The original description and figures are 

 misleading in that the second setiger v/as not distinguished from the 

 first; thus the stout spines referred to on the so-called first segment 

 were those of the second segment; the two segments are close to- 

 gether and easily confused. The so-called median cirrus of the first 

 segment was probably the prostomial caruncle or crest (not available 

 for examination) . The slides of the parapodia, from setiger 5 on, show 

 some of the stouter penicillate acicular neurosetae in addition to the 

 capillary neurosetae, evidently overlooked by Webster and Benedict. 



Disoma franciscanum Hartman (1947a) was said to differ from D. 

 multisetosum in the absence of a long cirrus on the third parapodium 

 as shown by Oersted (1844, fig.ll). The cirrus-like structure shown on 

 the figiu-e is confusing; it m^ay refer to the upper lobule of the fim- 

 briated notopodial postsetal lobe, which is often larger and may be set 

 apart somev/hat from the other lobides (it was previously pointed out 

 by Mesnil that Oersted confused the dorsal and ventral sides of the 

 animal). In examination of the types of D. franciscanum, I was un- 

 able to detect any embedded acicula such as those figured by Hartman 

 (1947a, fig. 2,a,d). 



Description. — Length up to 90 mm. or more, width up to 5 mm., 

 segments up to 200. Body long, subcylindrical, anterior thoracic re- 

 gion wider, flattened dorsoventrally, rest of body flattened ventrally, 

 arched dorsally, tapering gi'aduaUy posteriorly. Body fragile, break- 

 ing up easily. Prostomium (fig. 82, a-c) elongate oval, wedged between 

 parapodial lobes of fii-st setiger, anterior two-thirds flattened, may ex- 



