90 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



Diagnosis. A genus of Thalassometridae in which the arms are dorsally rounded 

 to the tip; the arms in fully developed individuals are more than 15 (normally 20) in 

 number, with the IIBr series 4(3+4), exceptionally 2; the division series are smooth 

 and without spines though the lateral edges of the ossicles may be everted and tuber- 

 cular or serrate; the first syzygy following a IIBr 4(3+4) series is between brachials 

 3+4; the cirri are recurved distally, the outer segments carinate or with dorsal spines; 

 and the genital pinnules are not appreciably expanded. All the included species are 

 large, full sized individuals having the arms 110-160 mm. long. 



Geographical range. From Formosa (Taiwan) and the Philippine Islands south- 

 ward to the Moluccas and westward to the Maldive and Laccadive Islands and south- 

 eastern Africa from Durban to Port Elizabeth. 



Baihymetrical range. From 55 to 2,047 meters. 



Remarks. When fully developed the species of Crotalometra are quite distinctive 

 and are not easily confused with the species of any other genus, the large size, 20 or 

 about 20 arms with the IIBr series 4(3 + 4), and the long and stout cirri giving them 

 a characteristic appearance. Much depends, however, on the condition of the pre- 

 served specimen. If the arms are extended parallel with each other so that the division 

 series are fully visible and in contact a specimen of any of the species is unmistakable. 

 If, however, the arms are recurved over the centrodorsal the appearance changes 

 completely so that in most cases an analysis of the characters becomes necessary. 



Three species of Crotalometra are recognized herein sentifera, rustica, and magni- 

 cirra. As synonyms under rustica are included infelix, marginalis, and eridanella, the 

 type specimens of which do not seem to differ from rustica to any significant degree. 



The only reliable feature for specific differentiation in the genus Crotalometra 

 appears to be the relative production of the distal dorsal edge of the outer brachials. 



History. The first known species of Crotalometra was described under the name of 

 Antedon magnicirra by Prof. F. Jeffrey Bell in 1905. At the time I published my first 

 revision of the genus Antedon in 1907 I had not been able to consult the description of 

 Antedon magnicirra, but in a paper published on April 11, 1908, 1 referred it to the genus 

 Thalassometra. The generic name Crotalometra was first used in a paper published on 

 April 17, 1909, in the combination Crotalometra rustica, sp. nov., under which heading 

 this species was described. The genus Crotalometra therefore dates from this appearance 

 of the name, with C. rustica as the genotype. In a paper on new Philippine crinoids 

 published on May 13, 1909, but submitted for publication in advance of the paper just 

 cited, the new genus Crotalometra is diagnosed, and the genotype is given as C. eupedata, 

 new species, the description of which follows. Under Crotalometra I said: 



Carpenter's Anledon valida, the systematic position of which has puzzled me greatly, belongs to 

 this genus, and is closely related to C. eupedata, though apparently perfectly distinct; Anledon incerla 

 also should be referred to this genus. The Antedon magnicirra described from South Africa by Professor 

 Bell is likewise a member of this genus, and I have examined two or three additional species from the 

 East Indian region. 



In a paper on the Recent crinoids of the coasts of Africa published on March 15, 

 1911, I listed and gave the ranges of Crotalometra magnicirra, C. porrecta, and C.flava 

 (the last two herein referred to the new genus Koehhrmetra) . In my memoir on the 

 crinoids of the Indian Ocean published in 1912 I gave the range of Crotalometra as from 

 the Kermadec and Meangis Islands to the Philippines in 340-630 fathoms, and listed 



