10 THOS. H. MONTGOMERT, 



of which connects the two eyes of a side, and passes posteriorly to 

 the end of the body. Each of these bands is frequently of such 

 width aud intensity of coloration, as to be easily seen with the naked 

 eye. But quite often, more especially in young individuals, the pig- 

 ment bands are more or less indistinct and not continuous, with the 

 pigment of a less intense color and amount; which bring us to in- 

 dividuals in which almost no evidences of these markings are to be 

 found. The position of the eyes and shape of the head, which Verrill 

 has described, are, however, always good criteria for determining the 

 species. 



I found this species to be quite numerous among sea-weeds in 

 Ludlam Bay, Sea Isle, though not as abundant as T. flagellatum. 



6. Tetrastemma vermictilum (Quatr.). 



The commissure of the lateral nerve chords lies above the in- 

 testine, at the posterior end of the body, 



The Oesophagus opens into the rhyuchodaeum. The intestinal 

 coeca extend to the dorsal brain lobes. 



Sensory hairs are absent in the body epithelium; the pigment 

 of the head region is contained in the supporting cells (cf. T. elegans 

 and T. catenulatum). 



The cephalic gland is not very voluminous, and extends only to 

 the brain. 



The rhynchocoel extends to the posterior end of the body. The 

 central stilet of the proboscis is rounded basally, and slightly con- 

 stricted medially, though the medial constriction is not infrequently 

 absent (as in Fig. 25, which represents an abuormally large stilet 

 basis, Figs. 17—22, 24, 25 being drawn under the same scale of 

 magnification). The stilet basis apparently increases with the age of 

 the individual; but since in very large individuals, the size of the 

 stilet basis is not infrequently very small relatively, it would seem to 

 be not unusual for it to be cast off, and for a new one to be pro- 

 duced. A very abnormal accessory stilet from one of the lateral 

 pockets is reproduced in Fig. 26. There are two of these lateral 

 pockets, each of them usually containing three stilets. I have noticed 

 the followiug variations in the number of the stilets in both pockets: 

 2 — 1, 3 — 3 (average number), 5 — 5, 



2-2, 4-4, !5- 6, 



2—3, 4-5, 4- 8, 



2—4, 4-6, 5-11. 



