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. Eoy. Belg. xxii, pt. ii, 1855, p. 549. 



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

 dee]} grooves on each side; branchiae rather short. Hearts usually four in number. 

 Hab. — Europe. 

 BousEiELD (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 (Lbidy). 



Aulophorus vagus, J. Lbidy, Am. Nat. i880j p. 423. 

 D. vaga, L. Vaillant, Annel^s, p. 383. 



Definition. Length, about 8 mm. ; number of segments, 25. Hody 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 VIII, IX, X. Hab. — N. Am.erica ; Trinidad. 



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



and illustrated by Keighakd. 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. Stieeen received examples from Trinidad. 



(7) Dero latissima, Bouspield. 



D. latissima, Bousfield, Kep. Brit. Ass. 1885, p. 1098. 



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

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



