Si/nopsls of the Australian Calcarea Heterocosla. 95 



paired angles and the basal ray may be either longer or 

 shorter than the other two, which measure, say, abont 0"09 

 by ()0()8 mm. ; tlie apical ray is well developed, conical, 

 gradually sharp-pointed, slightly curved, and nearly as long 

 and thick as the oral ray.s. These spicules form such a 

 dense feltwork that it is difficult to make out the details of in- 

 dividual form in situ, while the projecting apical rajs thickly 

 echinate the gastral cavity. {'2) Quadritadiates of the exha- 

 lant canals ; these are extremely characteristic and peculiar 

 spicules ; the basal ray is reduced to a mere rounded 

 tubercle, while the oral and apical rays are long, straight 

 and very slender, and finely pointed ; the oral rays diverge 

 at an angle of about 120" and the apical comes off between 

 them and appears to lie nearly in the same plane ; the 

 oral rays measure about 008 by 0027 mm., though 

 occasionally stoutei*, and the apical ray is about one-third 

 as long ; these spicules ai'e found around the exhalant canals, 

 with the apical ray projecting into the cavity. A few lai-ger 

 and stouter quadni-adiates, with normal basal ray, also 

 occur around the exhalant canals. (3) Inner sagittal tri- 

 radiates ; under this term we may pei'haps, in this species, 

 include all those triradiates which lie in the zone between 

 the gastral cortex and the commencement of the flagellated 

 ■cliambers, although they lie at varying depths beneath the 

 gastral cortex. The oral rays are straight or nearly so, conical 

 and gradually sharp-pointed, about 0-09 by 0-0085 mm.; the 

 basal ray is long, straight, conical and gradually sharp- 

 pointed, measuring about 0- 1 6 by 0-0085 mm. ; the oral angle 

 is wider than the paired angles. (4) Tubar triradiates ; 

 very similar to the foregoing but the basal r;iy gradually 

 diminishes in length towards the dermal cortex. These 

 spicules form an articulate tubar skeleton of many joints, 

 which is continued, as already indicated, within the inner 

 limits of the chamber layer to the gastral cortex, while 

 towards the outside it becomes irregular and gradually 

 passes into the skeleton of tiie dermal cortex. (5) Triradiates 

 of the dermal cortex ; slightly sagittal or sub-regular, 

 mostly larger and stouter than the tubar triradiates, with 

 conical, sharp-pointed rays measuring about O'l 6 by 0-02 mm., 

 but very variable ; towards the outside they lie parallel to 

 the dei-mal surface, but otherwise they are very irregularly 

 arranged. (6) Large oxea of the dermal cortex ; fusiform, 

 slightly curved, gradually sharp-pointed at each end ; 

 measuring about 1-4 by O'l mm., but sometimes more or 



