CALCAREOUS SPONGES. 731 



There is certainly no indication whatever of the genus Leucetta 

 having passed through a syconoid stage in its evolution, as we 

 believe to be the case with the true Leucandras and Leucillas, 

 and we therefore propose to re-establish this genus for certain 

 leuconoid Leucascidse. 



We have also placed in this family the genus Pericharax 

 Polejaeff [1883], on account of the similarity of the skeleton and 

 the basal position of the nucleus in the collared cells, while the 

 genus Leucoinalthe can only be placed here provisionally. 



It should perhaps be mentioned here that von Lendenfeld's 

 genus Leucopsis [1885 B] was also supposed by its author to 

 represent a "Transition form between AsconidsB and Leuconidae." 

 The genus, with its single species, Leucopsis pedimcidata, was, 

 however, so imperfectly described that it is impossible to form 

 any definite opinion as to its systematic position ; it is very 

 possibly merely a reticulate Leucosolenia with well developed 

 mesoglcea and pseudogaster, an opinion which is supported by an 

 examination of some of von Lendenfeld's type specimens, which 

 one of us was able to make in Berlin. At all events, it appears 

 to differ widely from any of our Leucascidse, and it has been 

 placed by us among the Leucosolenias. 



We have been able to determine the position of the nucleus in 

 no less than ten species of this small family, including five species 

 of Leucetta, and in all cases have found it basal, a fact that affords 

 strong support to our view that the genus Leucetta should be very 

 widely separated from Leucandra, in which the nucleus is, so far 

 as we are aware, always apical. 



Genus 5. Leucascus Dendy [1892 B]. 



Diagnosis. Flagellate chambers greatly elongated, tubular, and 

 sometimes copiously branched. 



For illustrations of this genus see Dendy [1893 A]. 

 We recognise the following species in this geniis : — 



Section A. Without oxea. 



1. L. INSIGNIS Row. 



Leucascus insignis Row [1913 MS.]. 



2. L. SIMPLEX Dendy. Type species of the genus. 



Leucascus simplex Dencly [1892 B]. 



Section B. With lai-ge radially arranged oxea. 



3. L. clavatus Dendy. 



Leucascus clavatus Dendy [1892 B]. 



