380 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
Isoactinate. When both actines of a diactinal spicule are alike in shape and size, the spicule is said to 
be isoactinate. 
Isochela. A chela in which the two ends are alike and equal. Figs. 3, 4. 
Main or primary fiber. A principal liber of the skeleton, directed radially to the surface or extending 
longitudinally through the body. 
Megasclere. One of the larger spicules which compose the supporting 
skeleton. 
Microsclere. One of the small spicules scattered irregularly through the 
body in many sponges. 
Microxea. A minute oxea. 
Monactinal. Term applied to a uniaxial spicule in which growth pro- 
ceeds in only one direction from the point of origin. Thus only 
one ray is formed, the point of origin remaining at the end of 
the spicule, which may or may not be swollen. 
Orthodixne. A reduced Orthotrisene in which the cladome includes but 
two rays. Fig. 7. 
Orthotrisme. A trisene in which the cladi make about a right angle with 
the rhabdome. Fig. 8. 
Oxea. A uniaxial spicule gradually pointed at each end. Fig. 9. 
Oxyaster. Euaster with small centrum or none, and in which the rays 
taper to points. Fig. 14. 
Oxyhexaster. Hexact, principal rays of which divide into straight or 
bent terminals, which run out to a point. Fig. 11. 
Palmate. Vide chela. 
Parenchyma. Vide ectosome. 
Pentad. Spicule with five rays; a reduced hexact. Fig. 12. 
Plagiotrixne. Trisene in which the cladi are directed forward, making an 
angle of about 45° with the rhabdome produced. 
Polyserial. Arranged in several rows. 
Primary fiber. Vide main fiber. 
Protocladus. Vide dichotrixne. 
Prolrixne. Trisene in which the cladi are directed forward, making an angle of less than 45° with the 
rhabdome produced. Fig. 13. 
Rhabdome. Shaft of a trisene. 
Rhabdus. A rod-like, uniaxial spicule; with like or 
unlike ends. 
Rhaphide. A long hair-like spicule. Fig. 10. 
Sagitta. Vide trixne. 
Sanidaster. Microsclere consisting of a rod-like axis, 
bearing spines along its whole length. 
Fig. 15. 
Sclere. Skeletal element or spicule. 
Secondary fiber. A fiber extending directly or indi- 
rectly (as part of a reticulum) between two 
main fibers. 
Sigma. Microsclere shaped like the letter “c.” 
Fig. 16. 
Sigmaspire. A rod-like microsclere spirally twisted. 
Fig. 17. 
Sornal. Said of microscleres which are found both 
in ectosome and choanosome. Such spicules 
often give the impression of belonging pecu- 
liarly to the ectosome. 
Sphserohexaster. Hexact, principal rays of which divide into terminals provided with. spherical knobs 
at the ends. Fig. 18. 
Spheraster. Euaster in which centrum is large as compared with length of the rays. Figs. 19, 20. 
Spherule. A minute microsclere, more or less spherical in form. Fig. 21. 
8. Orthotriaene. 
9. Oxea. 
10. Rhaphide. 
11. Oxyhexaster. 
12. Pentact. 
13 
13. Protrirene. 
11. Oxyaster. 
