52 CAULOPHACUS SCHULZEI. 



connecting their ends, and 7-26 m thick near the middle. The central tyle 

 measures 11-32 fi in transverse diameter and is 2-9 ti, on an average about 4.4 yu, 

 thicker than the adjacent parts of the spicule. In the central tyle a transverse 

 cross is observed, composed of four rudimentary axial tlireads, about 1 ii long. 

 At the ends, these rhabds are 0-4 ju thinner than near the centre. Their aniso- 

 actinity is not great, the difference in the thickness of the two ends usually not 

 exceeding 2-3 m- The terminal spiny regions are 20-45 n long. The spines in 

 them stand close together, attain a length of about 1 ti, and arise vertically. 

 They are either straight or slightly curved backwards, towards the middle of 

 the rhabd, at the end. 



In comparing the measurements of the rhabds of the body of the small 

 specimen (with a disc about 30 mm. in diameter) with those of the rhabds of 

 the large specimen D (with a disc about 60 mm. in diameter), I found no per- 

 ceptible difference in their length, but a well-pronounced difference in their 

 thickness, the body-rhabds of the 30 mm.-specimen B being 10-21 /x thick and 

 having central tyles 15-26 n in diameter; those of the 60 mm.-specimen D being 

 10-26 M thick and having central tyles 16-32 /i in diameter. 



Wilson {loc. cit., p. 45) states that in the specimens examined by him the 

 rhabds were 1-4 mm. long, usually 1.5-2.5 mm.; 8-12 yu thick, exceptionally 

 24//; and " subterminally roughened with microtubercles." To me the sub- 

 terminal protuberances appear as sharp-pointed spines and I should not call 

 them "microtubercles." 



The hexadine megasderes of the dioanosome (Plate 7, figs. 20-31) measure 

 1.2-3.2 mm. in total diameter. The rays of the same hexactine are fairly equal 

 in thickness but differ more or less, often very considerably, in length. In 

 many hexactines the longest ray is two to three times as long as the shortest. 

 The rays are 250 /i-1.4 mm. long, conic, blunt, 25-74 yu thick at the base, and 

 7-18 fi just below the end. They are more or less, often considerably, curved, 

 rarely angularly bent (Plate 7, fig. 28). The long rays are invariably smooth 

 and attenuated toward the end. The rays reduced in length are either conic, 

 pointed, and spiny (Plate 7, fig. 21) or, more rarely, cylindrical, terminally 

 thickened, and smooth (Plate 7, fig. 29). 



In the shortened conic and spined rays there is a correlation between the 

 number and size of the spines on the one hand, and the degree of longitudinal 

 reduction of the ray on the other, the development of the spines being in pro- 

 portion to the degree of reduction. Here, as in the similar case of Calycosilva 

 cantharellus, this correlation between spine-development and reduction in length 



