216 PROF. W. B. BENHAM ON AQUATIC [NoV. 3, 



but how far the number is liable to variation is a subject that has 

 received but little attention. In my specimens they are pretty 

 constantly 4 ventrally and 3 dorsally, except the very anterior 

 ones. At any rate, Vejdovsky's figm^e (pi. viii. fig. 22) gives a 

 form very difierent from that of the new species ; for the upper 

 tooth is not pouited, but blunt, and much larger than the lower 

 tooth, the proportions being very different from those in my 

 species. 



The presence of a single pair of hearts in this and the following 

 species, which, at any rate in L. vejdovshyamis, have a peculiar 

 form and arrangement, would appear to demand the creation of a 

 new genus for this worm ; for Michaelsen, in ' Das Tierreich,' gives 

 two pairs of hearts in segments viii. and ix. as a character of the 

 genus Limnodrilus. But in the character of the chastse, and still 

 more in the chitinous penial tube, this species agrees so precisely 

 with Limnodrilus, that I deem this procedure unnecessary. 



Limnodrilus lucasi, sp. n. (Plate XXY. figs. 18-22.) 



A slender worm with thick body- wall ; the segments are not 

 annulated. 



The prostomium is short and rounded ; the peristomium is as 

 long as segment ii. 



The chcetce are 5 in each bundle in the most anterior segments 

 (ii,, iii., iv., v.), then diminish to 4 ; and later (in segment x. and 

 posteriorly) to 3 in each bundle. 



The dorsal and ventral chsetse on segment ii. are rather shorter 

 than on the other segments. All the chsetse are alike ; the prongs 

 or teeth are nearly equal in length, but the lower or proximal 

 tooth is slightly the stouter, and in the posterior segments it is a 

 trifle longer than the lower prong. But even in one and the same 

 bundle the relative length of the two prongs exhibits various 

 proportions. 



Yentral chsetee are present on segment xi. even in the adult. 

 The clitellum occupies two segments, extending from ^ x. 

 to ^ xii. 



Internal Anatomy. 



'The pharynx extends through segments ii, and iii. ; the chlora- 

 gogen granules are dark brown and commence in segment v. 



A large heart exists in segment viii., but I have not been able 

 to make out, in the entire individuals, the exact relations of this 

 organ. The blood has accumulated in the vessels at the posterior 

 end of the body, and the vessels are empty anteriorly. I did not 

 investigate this species by means of sections. The usual undu- 

 lating commissural vessels are present in the anterior segments, 

 biit I find no integumental vessels. 



The dorsal blood-vessel shifts from its pi-oper position in the 

 intestinal region, and takes up a lateral position as in Branchiura 

 sowerhyi (which, according to Beddard, is the only instance 

 amongst the Turbificidse of this arrangement). 



