112 GEODIA MESOTRIAENA. 



DIFFERENCES BETWEEN THE THREE VARIETIES OF GEODIA MESOTRIAENA. 





Var. pachana 



Var. megana 



Var. microana 



Shape 



meandric 



more solid 



more solid 



Large clioaiiosomal 

 amphioxes 



5.5-7.1 mm. long, 75- 

 105 /i thick 



5.3-8.2 mm. long, 70- 

 105 n thick. 



4.3-7.8 mm. long, 50- 

 77 /( thick. 



Small dermal rhabds 



420-6S0 /( long, 10-19 /i 

 thick ; styles numerous 



335-571 /I long, 10-18// 

 thick; styles rare. 



380-550 /( long, 9-15 /( 

 thick; styles rare. 



Ortho- and iilagio- 

 t riaenes 



chiefly plagiotriaenes ; 

 rhabdome 4.6-6.8 mm. 

 long, at cladome 85-115 

 /(thick; clades 250-660 /i 

 long; clade-rhabdomo 

 angle 94-108°, average 

 99.4°. 



chiefly orthotriaenes; 

 rhabdome 6.1-7.2 mm. 

 long, at cladome 90-120 

 /! thick; clades 200-670 

 /( long; clade- rhabdome 

 angle 85-96°, average 

 91.9°. 



chiefly plagiotriaenes; 

 rhabdome 5.7-7.2 mm. 

 long, at cladome 75-100 

 /( thick; clades 320-030 

 long; elade-rhabdome 

 angle 95-117°, average 

 104.2°. 



Me.soprotriaenes 



rhabdome .6-14 mm. 

 long, at cladome 15- 

 40 /i thick; epirhabd 

 95-230 /< long; clades 

 90-230 /I long; clade- 

 epirhabd angles 29-56°, 

 average 43.7°. 



rhabdome 8.8-11 mm. 

 long, at cladome 18- 

 40 // thick; epirhabd 

 140-330 fi long; clades 

 140-310 /( long; clade- 

 epirhabd angles 35-53°, 

 average 43.5°. 



rhabdome at cladome 

 17-22 /( thick; epirhabd 

 100-300 /( long; clades 

 130-210 /( long; clade- 

 epirhabd angles 35-54°, 

 average 40°. 



Anatriaencs 



rhabdome 11-16 mm. 

 long at cladome 27-40 /( 

 thick; clades 90-170 /< 

 long; clade-chord rhabd- 

 ome angle 39-56°, av- 

 erage 48.2°. 



rhabdome 15 mm. long, 

 at cladome 22-38 /< thick ; 

 clades 160-270 mm. 

 long ; clade-chord rhabd- 

 ome angle 34-58°, av- 

 erage 45.2°. 



rhabdome 1 1 mm. long, 

 at cladome 8-25 /( thick; 

 clades 70-175 mm. long; 

 clade-chord rhabdome 

 angle 39-55°, average 

 47.9°. 



Small strongylo- 

 sphaerasters 



Total diameter 8.2- 

 14.5 /( 



total diameter 6—14 /i. 



total diameter 7.5—14 //. 



Oxyasters 



total diameter 17-37 /i 



total diameter 17-54 /t 



total diameter 11-42 fi. 



Oxysphaerasters 



total diameter 20-30 jj. 



total dianieter 19-32 /i 



total diameter 26-27 /(. 



Sterrasters 



102-125 n long, 90-102 fi 

 broad, 75-82 /i thick; 

 average proportion of 

 length to breadth to 

 thickness 100:91:70. 



100-1 15 /(long, 80-105 /X 

 broad, 75-82 /t thick; 

 average proportion of 

 length to breadth to 

 thickness 100:90:71. 



92-120 /( long, 78-107 /( 

 broad, 67-78 n thick; 

 average proportion of 

 length to breadth to 

 thickness 100:79:71. 



praeoscular cavities, differently shaped small strongylosphaerasters, and much 

 smaller megascleres and choanosomal oxyasters. Geodia hreviana also has much 

 smaller megascleres; this species is also distinguished from G. mesotriaena by 

 its minute, dermal anaclades and the thickness of the clades of the large ana- 

 triaencs. The species most nearly allied to G. mesotriaena are G. mesotriaenella 

 and G. ovis. Of G. mesotriaenella there is only a small specimen in the collec- 



