54 NEMATODES OP THE GENUS PHYSALOPTEEA, 



even when all the required measurements are given, which is rarely the case. 

 And, where a long series of what is undoubtedly the one species is carefully 

 examined, similar variations are found to occur, both in the proportions and 

 conformation of organs. 



So that it is not advisable to rely on this character alone, although a very 

 necessary one, for a specific determination. Another objection to it is that it 

 usually requires the dissection of the specimens, a delicate and tedious operation 

 in the smaller species. 



A useful and more easily observed character is found in the structure of the 

 male caudal bursa. Seurat is of the opinion that the number and disposition of 

 the genital papillae are too constant to make this feature of specific value. But 

 a careful study of the male tails of all the species shows well marked differences, 

 not only in the papillae, but in the general shape and proportions of the bursa, 

 form of margin (whether lobed or straight), shape of cloaca and character and 

 arrangement of the area of cuticular granulations which usually surrounds it. 

 Such distinctions are well seen, for example, in a comparison of the caudal 

 bursas of Physaloptera mitarctica, P. sonsinoi, and P. dentata, shown in the 

 text figures. 



It appears, too, that a more thorough examination than is usually given to 

 the formation of the labial teeth would supply characters of specific value. In 

 the existing descriptions of the species, there are indications of marked differences 

 in the shape and size of the teeth, and in the denticular fonnations. 



In the following specific diagnoses, I have been careful to note, from the 

 authors, all those points in the descriptions which appeared to me to be of some 

 specific value, omitting features which have been described as common to all. 

 The measurements are gi'ouped all together, in a table, as they are essential for 

 specific determinations, and of most use when they are most readily available for 

 comparison. The figures of the male tails are also grouped together, for the 

 same reason; and, as they supply all the neeessai-y information in regard to the 

 number and arrangement of papillae, this is omitted from the diagnoses, except 

 in cases where no figure of the bursa has been given by the author. The figures 

 given in this paper represent traced copies of the originals. 



It will be noticed that in several of the species the uterus is divided into 

 four branches, instead of the usual two. 



Seurat has separated the Physaloptera of reptiles into two groups, those 

 which have a female genital apparatus formed of four uteri and four ovaries, 

 viz. — Formes tetrahysteriennes, and those in which it consists of two uteri and 

 two ovaries, Formes didelphes. 



This grouping has been adopted here. But the more typical arrangement 

 of the genital apparatus has been assumed for species when no mention of it is 

 made in the descriptions relative to them; and it is possible that, with more 

 careful study, more species will be found to have the four-branched uterus. 



Though P. abhreviata is one of Rudolphi's original species, the type of the 

 genus is P. clausa, and Diesing's revised diagnosis of the genus Physaloptera in- 

 cludes the definite statement "uterus bicomis." It may be questioned, therefore, 

 whether species with four uteri are properly assignable to the genus; though it 

 would seem undesirable to establish a new genus entirely on a character which 

 can be determined only by dissection. 



Of the fifteen species which have been recorded from lizards, several have 

 already been proved to be synonyms, and there are reasonable gi-ounds for the 

 supposition that other names will fall as synonyms. The total number of valid 



