Crinoidea. 311 



The small species of tlie genus Zijgometra resemble closely certain of 

 tlie small species of the genus Heterometra, while the large species are 

 superficially extremely close to the similarly large species of the genus 

 Himerometra, even possessing the peculiar and characteristic arm structure. 

 Though the presence of a pseudosyzygy between the elements of the IBr 

 series is the essential feature differentiating the Zygometridae from the 

 Himerometridae, the actual determination of the individual species is best 

 made on the structure of the proximal pinnules, combined with the pres- 

 ence (Zygometridae) or absence (HimerometridaeJ of a platiug on the disk. 



Fam. Mariametridae A. H. Clark. 



Uichf'onietra f/ygcs (Bell). 



Plate IV, Fig. 3. 



1911. Dichrometra tenera, A. H. Clark, in : Die Fauna Südwest- Australiens, III, p. 4(30. 



1912. Dichrometra gyges, A. H. Clark, in Smithson. CoUect., LX, No. 10, p. 25. 



Notes: The three supposed species Dichrometra tenera (Hartl.), B. 

 gyges (Bell) and D reginae (Bell) are in reality the same form. 



In Plate IV, Fig. 5 I figure the extraordinary specimen with 57 arms 

 distributed among 7 rays mentioued in my first report upon the Crinoids 

 of the Hamburg West-Australian Expedition (1. c. p. 460), 



Fam. Colobometridae A. H. Clark. 



Petasometva A. H. Clark. 



1912. Petasometra n. g., A. fl. Clakk, in: Smithson. Collect., LX, No. 10, p. 25. 



Biag'iiosis : This genus is related to Decametra and to Cyllometra. The 

 arms are from ten to twenty or more in number, the IIBr series being 

 4 (3 + 4), rarely 2. Pa is always absent. Pi is as long as, and similar to, 

 Pg ; the following pinnules are shorter. 



Grcnotype: Antedon clarae Hartlaub, 1890. 



Bange : S h a r k s B a y , Western A u s t r a 1 i a , to A m b o i n a. 



JPetasonietra helianthoides A. H. Clark. 



Plate IV, Figs. 4 and 5. 

 1912. Petasometra helianthoides, A. H. Clark, in : Smithson. Collect., LX. No. 10, p. 26. 



Locality; Stat. 23, S h a r k s B a y , S o u t h P a s s a g e , 9 m ; 16. VI. 05 

 (Type-specimen). 



One fine specimen, which may be described as follows: 



Centrodorsal tliin discoidal, with a broad flat dorsal pole 4 mm in 



