NO. 1772. ANNELIDS OF THE ARENICOLID^—ASHWORTII. 



27 



The prostomium is well seen in only two of the specimens. It con- 

 sists (see fig. 12) of two large lateral lobes of almost uniform width 

 (i. e., they are not markedly dilated anteriorly), which unite pos- 

 teriorly to form a wide median portion of the prostomium. Between 

 the lateral lobes is situated the me- 

 dian one, which is small. Its trans- ' '• 



verse diameter is less than one-third 

 that of the whole prostomium and 

 its antero-posterior diameter is also N.uR: 

 short (about .5 mm.). The nuchal 

 organ exhibits the usual relations to 

 the prostomium. In the specimen 

 figured (from No. 5) the lip (L. N.) 

 of the nuchal organ is well everted. 



The an- 

 nulation 

 of tlie an- 

 terior re- 

 gion is rep- 

 resented 

 in the an- 

 nexed dia- 

 gram (fig. 

 13), which 



is drawn from specimens Nos. 1 and 2. 

 Each segment behind the third is divided 

 into five rings, the largest of which is the 

 chsetigerous one. 



Neuropodia are clearly visible on each 

 segment, even on the first one. (Compare 

 A. cristata.) The groove of the first neu- 

 ropodium is 0.3 to 0.5 mm. long and five 

 or six crotchets may be seen in it. The 

 neuropodia gradually increase in length in 

 successive segments ; that of the sixth seg- 

 ment is 2.5 mm. in length (in No. 1), 

 and in the branchial region the long mus- 

 cular ridges of the neuropodia become 

 more obvious. Those of the posterior seg- 

 ments extend from a point just below the 

 notopodium almost to the mid-ventral 

 line and their grooves are about 4.5 mm. 

 These posterior neuropodia are of the elongate type, seen 

 also in A. marina and A. cristata, and diff'er from those of A. clapa- 

 redii and A. assimilis, which are shorter and more or less oval cushion- 

 like pads. 



Fig. 12.— a. glacialis, anterior end, 

 dorsal a.spect. x6. l, lateral lobe 

 OF prostomium; L. iV", lip op nuchal 



ORGAN SLIGHTLY EVERTED; M, MEDIAN 

 LOBE OF PROSTOMIUM; iVl, FIRST NOTO- 

 PODIUM (THE NOTOPODIUM IS RETRACTED, 

 LEAVING A SLIT ON THE StTKFACE); N. OR, 

 NUCHAL GROOVE. 



fflG. 13.— A. GLACIALIS, DIAGRAM REP- 

 RESENTING THE ANNULATION OF THE 

 ANTERIOR END. X4. A", FIRST 

 NOTOPODIUM. 



long 



