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Show 216 TROF. 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 m y specimens they are pretty constantly 4 ventrally and 3 dorsally, except the very anterior ones. At any rate, Vejdovsky's figure (pi. viii. fig. 22) gives a form very different from that of the new species; for the upper tooth is not pointed, 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. vejdovskyanus, 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 chsetse, 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 XXV. 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 chaetae on segment ii. are rather shorter than on the other segments. All the chaetae 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. Ventral chaetae 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 undulating commissural vessels are present in the anterior segments, but I find no integumental vessels. The dorsal blood-vessel shifts from its proper position in the intestinal region, and takes up a lateral position as in Branchiura sowerbyi (which, according to Beddard, is the only instance amongst the Turbificidae of this arrangement). |
