300 OLIGOCHAETA 



is not found in the true D. obtusa. It is probably this species whose anatomy I 

 myself described (22). 



(5) Dero obtusa, D'UDEKEM. 

 D. obtusa, D'UDEKEM, Bull. Acad. Roy. Belg. xxii, pt. ii, 1855, p. 549. 



Definition. Number of segments, 50. Branchial area with distinct dorsal Up marked off by 

 deep grooves on each side ; branchiae rather short. Hearts usually four in number. 

 Hab. Europe. 

 BOUSFIELD (1) remarks that ' this species shows the first trace of the modification 



which leads to the formation of supplementary branchial processes in the distinct 



demarcation of the dorsal lip, at the angles of which they are borne by those 



species which possess them.' 



(6) Dero vaga (LEIDY). 



Aulophorus vagus, J. LEIDY. Am. Nat. 1880, p. 423. 

 D. vaga, L. VAILLANT, Annelds, p. 383. 



DeSnition. Length, about 8 mm. j number of segments, 25. Body ending in two long processes ; 

 branchiae rudimentary, only two slight processes. Dorsal setae bundles consisting of one 

 capilliform, and two pectinate setae. Perivisceral corpuscles present. Contractile hearts 

 in Fill, IX, X. Hab.N. America; Trinidad. 



This species, imperfectly described by LEIDY (10), has been more fully studied 

 and illustrated by REIGHAKD. The most marked characteristic of the species is the 

 very rudimentary condition of the branchia, and the existence of two long processes, 

 as in D. furcata. The vascular loops in the branchial region are correspondingly 

 simple. The dorsal vessel bifurcates a little in front of the tail, and joins a circular 

 vessel, which is again connected with the ventral vessel. On either side of the 

 point, where the ventral vessel arises, a slender trunk springs and forms a low loop 

 in the two rudimentary branchial processes, and there joins the dorsal vessel, just 

 after its bifurcation. The ' spade-shaped ' setae of the dorsal bundles are peculiar to 

 this species. Their outer ends are flattened, the expansion being supported by two 

 or three ribs. STIEKEN received examples from Trinidad. 



(7) Dero latissima, BOUSFIELD. 

 D. latissima, BOUSFIELD, Rep. Brit. Ass. 1885, p. 1098. 



Definition. Number of segments, 40. Four pairs of hearts. Branchial area with entire. 

 margin, wider than long ; branchiae lony. Hab. Great Britain. 



