II. A FAUNA WITHIN ANIMALS. 45 



body extending through 12 annul! ; intestine cylindrical, slightly dilated anteriorly, 

 narrowing posteriorly; rectum elongated, inverted pyriforra. Tail long, narrow, 

 conoidal, curved. Generative aperture near the middle of the body, slightly pro- 

 minent. 



Measurements. Length 2 lines ; greatest breadth jfa in. ; tail ^ in. long from 

 the anus ; anterior spinous portion of the body ^ in. long ; buccal organ -^ in. 

 long, -^ in. broad; gizzard yi^ in. long, with the breadth of its body ^ 7 in. 

 Anterior spines ^TsVff i* 1 - l n g- Ovum ^{ T in. long, ^\^ in. broad. 



Habitation. Found within the ventriculus of Passalus cornutus, adhering by 

 the mouth to the mucous membrane, most usually within the sacculi, and unless it 

 be scraped out, may escape detection. Three or four individuals are frequently 

 found within the short blind pouch at the commencement of the ventriculus. It 

 exists pretty constantly in numbers of two or three to twenty, rarely more. 



Although I have examined over a hundred individuals of Passalus cornutus, I 

 have never found a single male of Hystrignaihus. 



4. DESCRIPTION OF THE GENUS AND SPECIES OF STREPTOSTOMUM. 



STREPTOSTOmJM, LEIDT. 



Body cylindroid, with relatively few annuli, which are very long and distinct. 

 Mouth large, circular, without lobes or other appendages ; buccal organ and gizzard 

 pyriform. Female generative aperture posterior to the middle. Tail very long, 

 spiculate. Penis consisting of a single spiculum. 



I 



1. Streptostomum agile, LEIDT. 



Proc. Acad. Nat. ScL, iv., 230; and ib. v., 285. 



(PLATE VI. Fig. 5 ; VII. 2, 12.) 



Female. Body cylindroid, narrowed at the extremities, anteriorly conoidal, 

 divided into from 60 to 90 annulations. Oral annulus broad, with a prominent labial 

 margin; second annulus inflated at its anterior margin. Tail very long, very 

 straight, or slightly sigmoid, or bent at the distal extremity, linear, spiculate, ensi- 

 form, acute, shining, but slightly flexible. Mouth round, simple; buccal organ 

 robust, pyriform, extending through thirteen annuli ; gizzard robust, pyriform, with 

 its neck subdivided into a distinct subglobular portion, extending to the twenty- 

 first annulus ; intestine cylindrical, capacious, dilated oval at its commencement ; 

 rectum inverted pyriform. Generative aperture placed twenty-four annuli anterior 

 to the anal aperture. Ovary double ; ova oval. 



Measurements. Length of body 1 line ; breadth at commencement of intestine 

 j^-g- inch; at middle -fa inch. Tail -^ inch long by -gfa inch broad at the middle. 

 Buccal organ T ^ T inch long by |^ inch broad ; gizzard ^ 7 inch long by ^ TTr inch 

 broad. Ova T ^ inch long by %$-$ inch broad. 



