ON THE CLASSIFICATION OP THE EOTIFERA. 



27 



(b) The second form is a simple segment of a circle, placed on the ventral side 



above the mouth, fig. 22. 



(2) The Bdelloidio wreath is also of two forms : 



(c) The first, like the Bhizotic wreath (a), is a double wreath surrounding the body 



twice, and inclosing the mouth ; but, unlike the Bhizotic, it has two gaps 

 instead of one, viz. a dorsal gap between the points of flexure, and a ven- 

 tral gap in the upper wreath opposite to the mouth. 



(d) The second form of Bdelloidic wreath is a mere furring of the corona on 



its ventral surface, as shown in fig. 25. 



(3) The Ploimic wreath is very various in shape, but is never Bhizotic, while it is 

 Bdelloidic only in one genus. 1 



Fig. 23.— Bdelloidic wreath (c), 

 l mm above. 

 (Rottfer citrinus) 



Fig. 24.— Bdelloidic wreath (c), 

 side vie r. 



(Rotifer filritut-l) 



Fig. 25.— Bdelloidic wreath (rf). 

 (Adineta vaga) 



(4) The Scirtopodic wreath is of Bdelloidic type. 



III. In the form of the tropin. 



If we disregard two genera 2 of the Ploima (not one-fifteenth of the whole number 

 of Ploimic genera), we can then say that the first three orders differ also in the forms 

 of their tropin. For — 



(1) The Bhizotic tropin are either malleo-ramate, 3 fig. 26, or uncinate, 3 fig. 27. 



(2) The Bdelloidic tropin are always ramate, 3 fig. 28. 



(3) The Ploimic tropin are of various forms ; but are never Bdelloidic, and are 

 Bhizotic only in two genera. 2 



(4) The Scirtopodic tropin are of a Ehizotic type, being malleo-ramate, fig. 26. 



Fig. 2G. — Malleo-ramate. 

 (Afelicerta riivjew) 



Fig. 27. — Uncinate. 

 (Stephanoceros Eichhornii) 



Fig. 2s. Ramate. 

 (Rotifer citi inus ) 



Now, in reviewing the points of agreement and of difference in the four orders, we 

 may at once set aside the fourth order, the Scirtopoda, as unmistakably separated from 

 the others. 



This order contains but one family, which has only one genus, and that genus 

 itself consists of only one species. 4 In fact, it has been formed to contain that 

 remarkable creature Pedalion mirum, which I discovered at Clifton in 1871. This 



1 Ptcrodina. ■ Triarthra and Ptcrodina. 



3 For the explanations of these technical terms, see p. 29. 



* I pass over for the present Dr. Schniarda's Hexarthra polyptera, and will discuss it under the 

 Pedalionidcc. 



