SPONGES.-HALLMANN. 153 



atice. The smooth oxeotes are asymmetrical, and -Lvhen 

 they attain in the fullest degree their characteristic shape 

 are tornotoxea with a slight flexion at the tip of the 

 oxeote extremity. The extremes of the maximum dimen- 

 sions of the spicules in the knoum varieties are as fol- 

 lows: — Tornotoxea: Length, 160 to 220 m diameter, 4.^, 

 to 6 y. Echinating acantho style s : Length, 145 to 200 

 ft; diameter, 8 to 12 j^. Dermal acanthostyles : Length, 

 80 to 100 ]i; diameter, 5 to 8 ft. Isochelce arcuatcc : 

 Length, 16 to 2^ ji. 



The several sponges now to be described agree so closely in 

 the form and dimensions of their spicules that — despite con- 

 siderable differences in some other respects — it has been con- 

 sidered preferable to treat them as varieties of a single species. 

 Any differences that there may be in the shapes of the spicules 

 in the different varieties are too slight to be of diagnostic 

 value, and a single description will therefore suffice for all. 

 The megascleres are smooth oxeotes, and acanthostyles of 

 two kinds ; the microscleres are isochelse arcuatae of a single 

 kind. The oxea are slender, asymmetrical, slightly fusiform 

 straight spicules which in their very earliest stages of growth 

 appear to be monactinal. Their characteristic peculiarity — 

 which is usually, however, to be observed only in small pro- 

 portion of them — is a slight bending to one side of the tip of 

 one extremity. This peculiarity as it appears when most 

 highly developed, is illustrated in text-ligure 29, where it is also 

 to be observed that the spicule is most correctly described as 

 a tornotoxea. Throughout the descriptions they will be re- 

 ferred to merely as the oxea, or sometimes as the auxiliary 

 spicules. The extent to which they enter into the formation 

 of the fibre-core varies greatly in the different varieties ; in the. 

 variety digitata they are pretty well the sole constituents ; in 

 the varieties perramosa and levis they are mingled with a 

 variable proportion of acanthostyles; in the varieties arenacea 

 and rubra they are usually more or less completely supplanted 

 by acanthostyles. An interesting condition is found in the 

 variety pumila, where columns of oxea, descending down- 

 wards from the surface without admixture of acanthostyles, 

 form a common and characteristic feature of the skeleton. 

 The oxea also occur as interstitial spicules, but except in the 

 variety digitata are outnumbered as such by the accessory 

 acanthostyles ; in the last named variety also, they participate 

 in the formation of the dermal skeleton. The acanthostyles, 

 as previously mentioned, are of two kinds. Those which 

 predominate as echinating spicules and often in addition core 

 the fibres are straight conical spicules of variable length, pro- 

 vided with more or less recurved spines which are usually 



