WITH NOTES OX THE WEST INDIAN SPECIES. 257 



Subgenus 3. Ptychodera s. str. 



3. Ptychodera ruficollis n. sp. 



I was at first inclined to create a new subgenus for this well-marked species. 

 When a Ptychodera has no genital pleurae, like Pt. hedleyi, the only obvious external 

 character by which it can be recognised as a Ptychodera, is the presence of external 

 hepatic saccules. The present species differs from all other Ptychoderidae, in the 

 absence of these structures. This character, combined with the absence of pleural 

 folds and with the small dimensions and triangular shape of the branchial tract 1 , 

 renders this species as well-defined as could be wished. But it could hardly be identified 

 as a Ptychodera from its external features alone, and I am still in some doubt as 

 to the wisdom of not making a separate subgenus for it. Only two other Enteropneusta 

 have been described with a triangular branchial tract, namely, Pt. minuta and Pt. 

 sarniensis, from both of which Pt. ruficollis differs greatly. 



Colour, Measurements and External Form. 



Like other species of Enteropneusta the present form is characterised by a 

 peculiarity in its colour. There is a strong crimson element in the collar which 

 suggested the specific name. The colour of the proboscis in the living animal is 

 light opaque yellow ; that of the collar is dark reddish yellow, or yellow strongly 

 tinged or shot with crimson. This combination of yellow and crimson gives the 

 general effect of the colour known as Indian-red or Orange-red. 



The crimson colour of the collar is chiefly confined to its anterior free portion 

 and to the posterior region. The mid-region, which has the form of a circular cushion, 

 seen in front of the broad dark -coloured groove in Fig. 7, PI. XX VII., is generally 

 without the crimson and is dark yellowish. The extreme posterior marginal band or 

 so-called fifth zone of the collar is also free from crimson and is plain yellow. 



The ground-colour of the trunk is a dull subtranslucent yellow except in the 

 hepatic region, which is distinguished by- a bright brown colour. 



The proboscis is small and obtusely subcorneal in shape during life ; it measures, 

 in maximum extension beyond the rim of the collar, 4 — 4'5 mm. 



The collar is much longer than the proboscis ; its length is 6*5 to 7 mm., with 

 maximum breadth in its hinder region of 5 mm. The branchial region is remarkable 

 for its shortness, being sometimes even shorter than the collar; length 6 — 8 mm. 



The genital ridges, whitish in colour, commence at the posterior end of the 

 branchial region and extend back for some 50 — 60 mm., their maximum development 

 occurring close behind the branchial region. The genital region is therefore many 

 times longer than the branchial region — a good diagnostic feature. In Pt. hedleyi, with 



1 This is the " Kiemenfeld "' of Spengel and "gill-area" of Hill. 



36—2 



