CHAET0G2TATHA COLLECTED BY STEAMER ALBATEOSS. 239 



8. Anterior extremities of both pairs of fins rayless; anterior fin also rayless 



throughout a narrow strip adjacent to body; mature ovary long and 

 narrow, extending nearly if not quite to ventral ganglion S. serratodentata 



9. Tail 28-40 per cent of total length; posterior teeth 20-38, rarely as few as 17. 



S. macrocephala. 

 9. Tail less than 28 per cent of total length; posterior teeth rarely exceed 16.. 10 

 10. Posterior fins extend nearly if not quite to seminal vesicles; both pairs of fins 



rayed throughout 11 



10. Posterior fins never extend more than § distance from tail-septum to 



seminal vesicles; both pairs of fins rayless throughout a narrow strip 

 adjacent to body 12 



11. Body very transparent; interval between anterior and posterior fins always 



less than half the length of posterior fin S. setosa. 



11. Body semi-translucent but never transparent; interval between anterior and 



posterior fins usually greater than half the length of posterior fins S. elegans 



12. Vestibular ridge composed entirely of papillae; anterior teeth 0-4, rarely 5; 



posterior teeth 0-6 S. hexaptera. 



12. Vestibular ridge provided with usual skeletal parts; anterior teeth 5-12, 



rarely less than 6; posterior teeth 7-18, rarely less than 10 S. enflata. 



13. Collarette short, not extending over half-way from neck to ventral ganglion. 14 



13. Collarette long, extending more than £ distance from neck to ventral 



ganglion 22 



14. Anterior fins longer than posterior fins 15 



14. Posterior fins longer than anterior fins 18 



15. Posterior fins never extend nearly to seminal vesicles S. decipiens. 



15. Posterior fins extend nearly if not quite to seminal vesicles 16 



16. Body transparent; anterior fins exceed 30 per cent of total length of animal. 



S. pulchra. 



16. Body opaque or semi-translucent, but never transparent; anterior fins 



less than 30 per cent of total length of animal 17 



17. Both pairs of fins rayed throughout S. neglecta. 



17. Anterior extremities of both pairs of fins rayless «S. bedoti. 



18. Interval between anterior fins and ventral ganglion exceeds one-fifth length 



of fins S. bipunctata. 



18. Anterior fins extend nearly if not quite to ventral ganglion 19 



19. Collarette inconspicuous, extending less than one-fourth distance from 



neck to ventral ganglion 20 



19. Collarette well developed, extending between one-fourth and one-half 



distance from neck to ventral ganglion 21 



20. Pronounced constriction at tail-septum; sexually mature at a length of 



5-6 mm S. tenuis 



20. No constriction at tail-septum; never sexually mature under 9-10 mm. S.friderici. 



21. Anterior teeth 10-18; exceeding number of posterior teeth S. helenae. 



21. Anterior teeth 4-9; less than number of posterior teeth S. hispida. 



22. Collarette never extending to ventral ganglion S. neglecta. 



22. Collarette extending from neck to seminal vesicles S. calif ornica. 



22. Collarette extending fully to ventral ganglion, frequently onto anterior fins, 



but never beyond anterior quarter 23 



23. Posterior fins longer than anterior fins S. regularis. 



23. Anterior fins longer than posterior fins 24 



24. Less than 50 per cent of posterior fin in front of tail-septum S. ferox. 



24. More than 50 per cent of posterior fin in front of tail-septum 8. planktonis. 



KEY TO SPECIES OF SPADELLA. 



1. One pair of lateral fins entirely on tail-segment. Ventral transverse muscles 



present throughout entire body-segment S. cephaloptera. 



