HIRUDINEA ANU OLIG()CH.ETA OF THE GREAT LAKES RfXilON. 169 



Chaetogaster limnsei v. B:i r. 

 Chselogaster limniei. Wilcox, American Xattiralist, vol. xxxv. 19ul, p. ;iu5. 



The American examples of this species differ from the European in a number of minor points 

 which will probably require their eventual separation. Some of these differences have been alluded 

 to in Miss Wilcox's excellent description of the species. It is common about Philadelphia and was 

 well known to Dr. Leidy, by whom some excellent manuscript drawings were left, and has been 

 recorded by Professor Smith from Illinois. 



Many, both of parasitic and free-living individuals, are included in this collection from the follow- 

 ing stations: New Baltimore, Mich., August 14, 1893, several from Amnicola limom; Charlevoix, Mich., 

 August 6, 1894, from Limnsea stagnalis, many; Middle Bass Island, Ohio, North Swamp, July 21, 1899, 

 (105a), a large number. 



LUMHKICILID.I. 



Thinodrilus inconstans Smith. 



Thinodrilus incomtans Smith, Bulletin Illinois State Laboratory of Natural History, vol. IV, 1895, p. 292. 



In most respects these specimens agree exactly with Smith's description, but one example sec- 

 tioned has both anterior and posterior sperm sacs, the former beginning at the septum VIII IX and 

 reaching to VII, the latter beginning at X /XI and extending to XIV. The paired male orifices are in 

 X and there appears to be a small eversible penis, though it is retracted in all specimens. Five pairs 

 of very small spermathec;e occur in XII to XVI. None of the examples is mature. 



About a dozen of the largest examples are contained in an unlabeled vial belonging to the Lake 

 St. Clair collection, and a few fragments each occur in vials labeled (126) South Bass Island, Ohio, 

 near East Point, September 10, 189S, and (32a) East Swamp, South Bass Island, Ohio, July 10, 1899. 



TUBIFICID.€. 



Limnodrilus gracilis sji. nov. 



Form verj- slender and elongated, the length reaching ~r> mm. ; clitellum on XI and XII, but only 

 very slightly developed and none of the examples with enlarged genital region; number f)f somites, 

 140 to 175; prostomium flattened, moderately long. 



Setse anterior to X, 4 or 5, sometimes 3 or 6 per bundle; posterior to clitellum usually 2, occasion- 

 ally 3, and in the posterior fourth of the body only 1, in each bundle. On X the dorsal liundle usually 

 contains 3, the ventral 2 seta, and the glands which are associated with 

 the seta; bundles of all anterior somites are on this one better developed 

 than elsewhere. On XI ventral setie are usually absent altogether, their 

 place being occupied by the male genital orifices, while the dorsal bundle 

 is composed of 2 or 3 setae. All setje are hooked and bifid and have the 

 form shown in figure 5. Those on the genital and posterior somites have 

 the same shape as the others, but the latter are somewhat smaller. 



None of the specimens is nearly mature, but the reproductive organs 

 are sufficiently well developed to indicate their characteristic features 

 (fig. 6). Spermathecie, 1 pair in X, of fairly large size, reaching verti- 

 cally nearly to the dorsal wall of the body. They are of simple clavate 

 fiirm and, although the upper end is considerably inflated and has much 

 thinner walls than the lower half, there is no clear distinction between duct 



and pouch. The external opening is in line with the ventral setae, is Fig- b.—Limuodrilus grac. 

 simple and without glands or other special features. The spermathecje 

 are filled with elongated spermatophores having clear centers. Testes, 

 1 pair, attached on each side near the posterior base of the septum IX/X, long, slender, rising freely 

 into the dorsal part of the body cavity and reaching backward to the spermathecre. Male efferent 

 organs are not fully developed. Their deeply funnel-form crelomic ends are in X, with the mouth 

 opening directly clorsad. The vas deferens jierforates the septum X XI in line with the ventral seta 

 B. B. F. l»j— 12 



