408 Mr. 11. A. Baylis on a 



XLIV. — A neio Siamese Nematode of the Genus Falcaustra. 

 By H. A. Baylis, M.A. 



(Published by permissiou of the Trustees of the British Museum.) 



Falcaustra siamensisj sp. n. 



This worm, collected by Dr. Malcolm Smith from the gut 

 of the Siamese freshwater tortoise, Hieremys [^Cyclemys] 

 annandalei, and kindly presented by him to the British 

 Museum, shows a remarkable and interesting divergence 

 from the genotype, F. falcata (v. Liiist.), as redescribed by- 

 Lane (1915). This consists in the presence of a series of 

 sucker-like organs on the ventral surface of the caudal region 

 in the male, which will be referred to again later. In F. fal- 

 cata no such organs are present, and this point has been 

 confirmed by a re-examination of Lane's specimens, which 

 are in the British Museum. 



The worms (for measurements see table, p. 414) are stoutish 

 in the middle, tapering considerably at each end, and the 

 fixed material shows constantly a slight curvature towards 

 the ventral side at both ends in the female and a strong 

 ventral coiling of the caudal end in the male. The cuticular 

 striation is exceedingly fine. The lateral fields are con- 

 spicuous and attain a width of 0*35 mm. The musculature 

 of the body is of the meromyarian type of Schneider. 



The head (fig. 1) is somewhat wider at the base than the 

 neck which follows it. The mouth is bounded by three 

 similar lips (figs. 1 and 2), which are somewhat flattened 

 antero-posteriorly, except for two projections on each lip, each 

 projection bearing a rather prominent papilla at its apex. 

 The long nervous pulps of these papillae show the same bifur- 

 cation as in the type-species, but the inner branch is not 

 visible in a lateral view. When, however, the lips are seen 

 from the anterior aspect (fig. 2), the inner branch of each pulp 

 {N.P. 2.) is seen to run directly from its origin to the iiuier 

 border of the lip, where it seems to end in a little secondary 

 ])apilla. The mouth-cavity is surrounded, at the level of the 

 widest part of the head, by a thick cuticular ring (figs. 1 and 

 2, CM.), as in F. falcata. The bases of the pulps of the 

 cephalic papillee are seen (fig. 2) to be in close connection 

 with this, passing through six triangular apertures arranged 

 at regular intervals roinid the outside of the ring. 



The oesophagus shows the same parts as in the genotype, 

 differing only in relative proportions. The anterior division 



