8 PROCEEDINGS OF THE NATIONAL MUSEUM vol.72 



ventral portion of the mouth capsule, the medio-lateral and postero- 

 lateral rays are divergent, the cleft between these rays being deeper 

 tlian that between the externo-lateral and medio-lateral rays, whereas 

 in forms having two pairs of teeth in the anterior ventral portion of 

 the buccal capsule the medio-lateral and postero-lateral rays lie close 

 together and parallel, the cleft formed between these rays not being 

 deeper than that formed between the externo-lateral and medio- 

 lateral rays. 



The following key will serve to differentiate the species of Ancy- 

 lostoma'^ and to indicate their relationships. 



I. Three pairs of teeth in anterior ventral portion of buccal capsule; medio- 

 lateral and postero-lateral rays divergent. 



1. Inner pair of teeth small or rudimentary A. duodenale. 



2. Inner pair of teeth well developed. 



A. Species inadequately described; from an edentate {Dasypus 



gilvipes) A. miicronatum. 



B. Species adequately described ; from carnivores. 



a. Spicules 600^900 fi long A. caninum, 



1). Spicules l.S-22 mm. long A. conepati. 



II. Two pairs of teeth in anterior ventral portion of buccal capsule ; medio- 

 lateral and postero-lateral rays close together and parallel. 



1. Inner pair of teeth small or rudimentary. 



A. Three pairs of small toothlike projections present on dorsal wall 



of buccal capsule A. pluridentatum. 



5. Toothlike projections not present on dorsal wall of buccal 

 capsule A. braziliense. 



2. Inner pair of teeth well developed. 



A. Species inadequately described; from a primate {Mycetes 



coraya) A. mycetis, 



B. Species adequately described; from carnivores (Ursidae). 



A. malayauuiu. 



In connection with the above key it is worth noting that the teeth 

 in the anterior ventral portion of the buccal capsule of species of 

 AnoylostoTrm show a series of stages which may be interpreted as 

 being either progressive or regressive in nature. In A, caninum^ A. 

 conepati, and A. mucronatum three pairs of well-developed teeth 

 are present in the anterior ventral portion of the buccal capsule; in 

 A. duodenale the inner of the three pairs of teeth is very small, in 

 fact, almost rudimentary; in A. malofyan'mrh and, so far as can be 

 judged from Molin's figure, in A. tmjceth, only tAvo pairs of well- 

 developed teeth are present in the anterior ventral portion of the 

 buccal capsule; in A. 'pluridentatum and in A. ira^iliense two pairs of 

 teeth are present, the inner pair of teeth being reduced in size, the 



1 A. minimum is not included in this key owing to the ahsence of knowledge regarding 

 the presence of teeth in the anterior ventral portion of the buccal capsule. Assuming 

 that von Linstow's species belongs to the genus Ancylostoma, it has affinities with the 

 forms in Group II so far as can be judged from his figure of the bursa. 



