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PROCEEDINGS OF THE NATIONAL MUSEUM 



figures 1 and 2. Most often the spiral ends at the front of the telson, 

 but sometimes it appears in the midst of the series of abdominal rings, 

 with normal ruigs following it caudally. There may be two spirals m 

 one specimen (fig. 7 and pi. 7, figs. 1,2), and they may be right-handed 

 or left-handed. The largest spiral I have seen, consisting of a little 

 more than 4 complete turns, was observed in a large female of the new 

 species of Lepidurus (fig. 17), one of the two cases where the spiral 

 was found to affect the leg-bearmg part of the abdomen. It forms the 

 whole legless part of the body, too. A spiral usually begins in the 



body-ring 



Figure 7. — Ventral view of abdomen of a female of Apus granarius (Lucas) from China 

 (Stockholm Mus.) showing two right-handed spirals in the same specimen, both 

 beginning in the midventral line, the anterior one (Sp2) of two rounds and ending openly 

 at the midventral line, the posterior one (Spi) of a little more than one and one-half 

 rounds and with the distal end evenly tapering, X 14. (il/, muscle bundles indicated in 

 part of the body to show that their courses are not influenced by the spirals; i2, ridge 

 bordering the leg-bearing area; Spi, Sp2, spirals; 7", telson.) 



midventral or middorsal line, but in one case (fig. 4) it begins dorso- 

 laterally. The end of the spiral may be foimd in any place around the 

 periphery of the anterior margin of the telson and is often tapered 

 continuously for a rather considerable distance. If the spiral occurs 

 within the series of normal rings, it ends only midventrally or mid- 

 dorsally, in the cases which I have seen, and no long tapering has 

 been observed. 



