BY E. F. HALLMANX. 273 



numerous minute tubercles or spines; a few, however, have the 

 rays sharp-pointed and free from spines (oxyasters). In spite of 

 their many points of resemblance, the specimens nevertheless 

 exhibit certain decided differences, the most noteworthy of which 

 is in regard to the size of the sphei'asters; these attain a diameter 

 of 100 /x in one specimen, only Qb /a in another, and are of inter- 

 mediate size in a third. 



Tethya corticata. 

 According to its description, this species is characterised by an 

 irregularly conulated surface (apparently not incised by j)ore- 

 grooves), obtusely pointed styli of two sizes, the larger of which 

 attain a size of 2000 by 13/x, and micro.scleres of only two kinds, 

 spherasters and tylasters, the formei* abundant in the cortex. 

 The specimens indicated to be the types, however, as well as a 

 fragment labelled Tethya corticata from the British Museum, 

 while conforming fairly well with the description as regards 

 external features, have mostly sharp-pointed styli, the largest of 

 which measure 1600 by 28 /a, only moderately few spherasters, 

 and, in addition to (chiefly cortical) tylasters, abundant choano- 

 somal oxyasters, which are well distinguished from the tylasters 

 both in shape and size. They are, in fact, examples of a variety 

 of Donatia inyalli, differing in no essential respect from the 

 specimens labelled (correctly-, I feel sure) as the types of Tethya 

 /(cvis, except that in several of the latter, apparently merely in 

 consequence of individual variation, the megascleres which lie 

 free in the choanosome are notably of smaller size than those 

 which compose the fibres. One may, therefore, regard 2\ corti- 

 cata as synonymous with 2\ Icevis, and since the latter name 

 rests on a more certain identification than the former, it should 

 be preferred, and the sponge known as Donatia ingalli var. loivis. 



Tethya fissukata. (Plate xv., fig.3). 

 In addition to the several specimens referred to above in con- 

 nection with Tethya muItisteUa, the " types" of Tethya ^fissurata 

 comprise two specimens which are unquestionably to be iden tilled 

 with this species; yet, strangely, instead of being as the descrip- 

 tion states " irregularly spherical, more or less kidney-shaped 



