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THE VOYAGE OF H.M.S. CHALLENGEE. 



I. Subfamily 



Tripospyrida. 

 Three basal feet. (One • 

 odd caudal and two 

 paired pectoral.) 



Synopsis of the Gener-a of Zygospyrida. 



Apex of the shell with one horn, 



Apex of the shell with three horns, . 



Apex of the shell without horns, 



Apex with two large coryphal holes, right and left, . 



II. Subfamily 



Dipospyrida. 

 Two basal lateral feet. 

 (Originally the two 

 pectoral feet.) 



Two feet free, not grown 

 together. 



Feet simple, 



not branched, 



without lateral 



spines. 



One horn, . 

 No horn, . 



Two feet grown together and 

 uniting to form a ring. 

 Apex with a horn. 



Feet branched ^ , 



,., . > One horn, . 



like a tree. I ' 



Feet with a ] 



series of lateral \ One horn, . 



spines. ) 



Feet simple, . 



Feet with a series of lateral 

 spines, 



III. Subfamily 



Tetraspyrida. 

 Two sagittal and two 

 lateral feet. 



IV. SubfamHy \ 



Hexaspyrida. > 



Six basal feet. j 



V. Subfamily 



Pentaspyrida. 

 Five basal feet. 



VI. Subfamily 



Therospyrida. 



Four paii'ed lateral ■ 

 feet. (Two pectoral 

 and two tergal.) 



VII. Subfamily 



Polyspyrida. 

 Numerous (seven to - 



twelve or more) 



basal feet. 



VIII. Subfamily i 



Circospyrida. ^ 



No basal feet. ( 



Feet simple, not branched. 



Two sagittal, two pectoral, 

 and two tergal feet. 



I Apex with one horn, 



( Apex without a horn, 



Apex with one horn, 



Apex with three horns. 



Apex without a horn, 



f Apex with one horn, 



One caudal, two pectoral, and , ^ ^^j^ ^j^^^^ ^ 

 two tergal leet. ^ 



Apex without a horn. 

 Apex with one horn, .... 

 Apex with three horns (one apical and two frontal). 

 Apex with two lateral or frontal horns, 

 Apex without a horn. 

 Apex with one horn, 



Apex with three horns (one apical and two frontal). 

 Apex with numerous horns, . 

 Apex without a horn, 



Apex with one horn, .... 

 Apex without a horn. 



441. Tripospyris. 



442. Triceraspyris. 



443. Tristylospyris. 



444. CepJialospyris. 



445. Dipospyris. 



446. Brachiospyris. 



447. Dendrospyris. 



448. Dorcadospyris. 

 44&. Gamospyris 



450. Stephanospyris. 



451. Tetraspyris. 



452. Tessarospyria. 



453. Hexaspyris, 



454. Liriospyris. 



455. Cardharospyris. 



456. Clathrospyris. 



457. ^gospyris. 



458. Pentaspyris. 



459. Zygospyris. 



460. Elaphospyris. 



461. Taurosp>yris. 



462. Therospyris. 



463. Petalospyris. 



464. Anthospyris. 



465. Oeratospyris. 



466. Gorgospyris. 



467. Circospyris. 



468. Didyospyris. 



