56 rp:s?:arches in iipxminthology and pakasitology. 



Hab. — In the soft mud at the bottom of stagnant ditches and 

 ponds in the neighborhood of Philadelphia. 



Remark, — When drawn out of its concealment in the mud, it rolls 

 the posterior 3-4ths of the body into a spiral. 



9. Acetus Hyalhms, n. s. — Body cylindrical, posteriorly obtuse, 

 hyaline. Annuli 24 to 34. Podal spines anteriorly 3 to 4 in each 

 fasciculus, posteriorly in pairs, swollen slightly one-third their length 

 from the extremity, which is unguiform and bifurcated. Blood 

 faintly red. 



Length i >^ to 3 lines; breadth anteriorly i-333d inch; middle 

 i-28oth inch; posteriorly i-40oth inch. lyip i-5ooth inch long. 

 Podal spines i -550th inch long. 



Hab. — Found with the preceding, its anterior half buried in the 

 mud, and the tail rapidly vibrating like Saviuris or StrepJinris. 



Dero, Oken. 



Body vermiform. Podal spines in two rows. Lateral, setse. 

 Caudal appendages. Blood reddish. Proboscis and eyes none. 



10. Dero Limosa, n. s. — Body cylindroid, faintly reddish, translu- 

 cent ; 9, 16, 26, to 34 setigerous annulations when the body is in 

 from I to 4 divisions. Five anterior annuli without setse. Two 

 rows of podal spines ; 5 to 6 in each fasciculus anteriorly ; 3 to 4 

 posteriorly ; long sigmoid, bifurcate at extremity. Setae single, in 

 one row upon each side. Caudal annulation, expanded, truncated, 

 furnished upon each side of the anal aperture with four unequal, 

 compressed, oval curv^ed, contractile appendages. Upper lip trian- 

 gular. CEsophagus passing to sixth annulation. 



Length 2 to 6 lines ; breadth anteriorly i-ioth line ; middle i-8th 

 line; caudal annulation expanded i -5th line. Lip i -250th inch long. 

 Setae i -666th inch to i-i33d inch long. 



Hab. — Living in tubes of mud or decayed vegetable particles, 

 upon the bottom of stagnant ponds and ditches, in the neighborhood 

 of Philadelphia. 



It is usually observed with the po.sterior half or two-thirds of its 

 body projecting nearly vertically from its tube, with the caudal, 

 contractile appendages expanded. Upon any disturbance it rapidly 

 retreats within its tube. A sessile species of vorticella is frequently 

 found attached to the posterior part of the body. 



At first sight there appears to be only three appendages each side 

 of the anus, but closer examination proves the existence of a fourth, 

 small and not so distinct. 



