340 



Of the species which I have been able to examine I must refer the following 

 to this genus: S. Lansborovi Johnst., S. reticulata Mac Gilliv., S. trispinosa Johnst., 

 S. Jeffreysi Norman, S. unispinosa Waters, S. cheilostoma Manz., S. jacobensis Busk, 

 S. (Porella) malleolus Hincks, S. arctica Norman, S. majascula Smitt, S. porifera 

 Smitt, S. reticulalo-punctata Hincks, S. Smith Kirch., S. (Pseudoflustra) solida Stimps., 

 S. (Eschara) propinqua Smitt, S. (Lepralia) borealis Waters, S. (Schizoporelld) linearis 

 Hassall, S. (Schiz.) auriculata Hassall, S. (Schiz.) triangula Hincks, S. (Lepralia) 

 foliacea Ellis & Sol., S. (Lepralia) Otto-Maelleriana (= S. Pallasiana, var. projecta 

 Waters), S. (Lepr.) collaris Jullien (= Lepr. Pallasiana, var. strumata Waters) 

 and S. (Lepralia) Pallasiana Moll. 



While originally I only referred to this genus species with uniporous rosette- 

 plates, the aperture of which besides two well-developed hinge-teeth is provided 

 with a median tooth and the ectoooecium of which is provided with pores, for 

 instance S. Lansborovi, S. reticulata and S. trispinosa, I have been obliged gradu- 

 ally to extend the limits of the genus in the manner expressed in the above dia- 

 gnosis, seeing that the species in which the three characters named are constant 

 through transitions are connected with species which I was earlier inclined to 

 refer to one or more other genera. As to the rosette-plates a number of species 

 (e. g. S. linearis, S. auriculata, S. malleolus etc.) have on each lateral wall 3 — 5 

 uniporous plates while others (e. g. S. porifera, S. reticulato-punctata, S. solida, 

 S. Smitti) have 2 — 3 with 1—5 pores and a third group (e. g. S. propinqua, S. 

 foliacea, S. collaris and S. Pallasiana) have 1 — 3 with 6 — 30 pores, the number of 

 rosette-plates decreasing in inverse proportion to the number of pores in each 

 plate. A distinction between uniporous and multiporous rosette-plates cannot 

 therefore in these species be used as a generic character. A median tooth 

 which as systematic character is always more or less inconstant cannot be used 

 here either as a decisive generic character, as it is not always constant even 

 within the species. This applies for instance to S. solida and S. Smitti, in which 

 two species a median tooth may sometimes be present and sometimes absent. 



Quite apart from the fact that the proximal margin of the aperture in a 

 number of species is provided with a median tooth, it also shows considerable 

 differences in the form as well as in the breadth and the depth of its poster, 

 which is very often furnished with a more or less distinct sinus. The sinus is 

 narrowest in S. linearis and shows here considerable variation in forms from 

 different localities Whilst in a form from Bergen, for example, it is half as broad 

 as the aperture, in a form from Syracuse it attains only a fourth of the breadth. 

 To exclude all doubt as to these forms being connected, I may remark, that in 

 addition to both having the two lateral avicularia they are also provided with 



