1911] Michael: Chaetognatha of the San Diego Region. 33 



appearing more opaque. Tip of tail and especially the head 

 and ventral ganglion are much more opaque, presenting a dis- 

 tinct contrast to the body proper. Tail fin and lateral fins are 

 readily seen with the naked eye. 



Characters 



Body tiiniid, but does not always retain its form well. It is of much 

 the same consistency as S. hexaptera. Neck fairly well marked but not 

 so pronounced as in S. hexaptera. Body widest at a point from 50 to 60 

 per cent behind the head, usually corresponding in position with the 

 widest portion of the anterior fin. Lateral fields large. Muscles rather 

 weak and thin, as in S. hexaptera. Slight constriction at tail-septum. 

 Collarette absent. 



Anterior fin longer and narrower than posterior fin. Always extends 

 anteriorly nearly to the ventral ganglion, sometimes reaching beyond 

 the middle of that structure. Form subject to considerable variation, 

 but usually, in the San Diego specimens, an elongated acute triangle. 

 It is confluent with the posterior fin. 



Posterior fin extends caudally to seminal vesicles, when the latter are 

 tumid. Never less than 50 per cent of fin in front of tail-septum. Posi- 

 tion of greatest width is exceedingly variable, but is usually at or in 

 front of tail-septum. Semi-elliptical in form. Interval from anterior 

 to posterior fin is marked by the presence of a fin-bridge that renders 

 the two fins confluent. Width at narrowest part of bridge about 1 

 per cent. 



Vestibular ridge (pi. 3, fig. 16) consists entirely of papillae of the 

 same style as in S. hexaptera. They are high, rounded, and roughly semi- 

 circular in form being, in many casec, provided with a tooth-like pro- 

 jection (barb) at the apex. They are more numerous than the posterior 

 teeth, extending from beyond the external tooth to the near vicinity 

 of the mouth. The nature of the ridge is better shown in the accom- 

 panying table. 



TABLE 3 



Measurements of Vestibular Kidge of Sagitta lyra. 



Remarks 



^ Number of Extent of ridge k 



■5 -5 papillae in Microns j: 5 



aa ^ ' ' — ^ ' ' r^ §0 



oS -^B - £5 ^5 -g 



Is "^S a -^s ^-^ ?>*" -^ S-S a-s £^ (See pi. 3, fig. 16) 



1 40 4 12 3 5 909 585 169 154 Right ridge, papilla 3 and 6 with barbs 



1 40 4 12 3 5 846 523 154 169 Left ridge, papilla 1 and 2 with barbs 



2 33 4 14 3 5 831 477 169 184 Right ridge, papillae acutely tipped, no barbs 



3 37 3 12 3 6 800 538 154 108 Right ridge, papillae acutely tipped, no barbs 



4 37 4 11 2 5 800 462 154 184 Right ridge, papillae acutely tipped, no barbs 

 4 37 4 11 2 5 724 432 108 184 Left ridge, papillae acutely tipped, no barbs 



