126 Memoirs of the Indian Mî^seum. [Vol. II, 



second of these facts is unfortunate, but it is perhaps as well that too much stress 

 should not be laid on the cirri, at any rate in minute species, for these can only be 

 examined properly in such species under a high power of the microscope and in condi- 

 tions which render distortion and breakages difficult to avoid. 



The soft parts of the three allied species D. cor, D. siniiata and D. angulata exhibit 

 a close general similarity, but afford sound means of diagnosis as regards particular 

 organs. In fully adult individuals the characters of the penis especially appear to be 

 fairly constant. In D. simiata this organ is comparatively slender, while in D. cor 

 and D. angulata it is very stout. As regards the two latter species the curious three- 

 pronged chitinous structures on the distal part of the organ in D. angulata afford 

 a ready means of separation. The arrangement of the hairs on the anal appendages, 

 moreover, although it is by no means constant, differs much more widely in the 

 separate species than it does among the individuals of any one of them. In D. cor 

 there is a dense apical tuft extending some distance down the posterior margin as 

 an uninterrupted fringe; in D. simiata there is no definite tuft at the tip, but the 

 distal edge of the organ bears a regular double row of some six or seven hairs (or 

 rather some twelve or fourteen, if both series are considered), which only extends a 

 short distance down the posterior margin, while in D. angulata there is, as in D. cor , 

 a definite apical tuft extending down the appendages behind as a fringe, but this fringe 

 is interrupted at one or more points. Differences in the maxillae, mandibles and other 

 mouth parts also exist, but are less reliable. 



