BRISSOPSIS LYRIFERA. 201 



the number of species in the genus can be considered as settled. The pedicel- 

 lariae are of little use in identifications of Brissopsis species, for they are very 

 variable and not particularly distinctive, but no study of the limits of their 

 diversity has yet been made. Even such apparently fundamental characters 

 as the number of plates in the subanal plastron, and the number of penicillate 

 tube-feet there, are subject to individual diversity to a perplexing degree, while 

 the form and direction of the petals is aggravatingly variable. In the face of 

 all the difficulties, it is not strange that the following key is unsatisfactory. 



Key to the Species of Brissopsis. 



Posterior petals divergent, primary tubercles approaching madreporite in interambula- 

 crum 5. 



Test truncate posteriorly; periproct vertical, scarcely visible from above; petals I 

 and V shorter than II and IV. 



Test more or less flattened; apical system subcentral; anterior margin of 



labrum .25-30 test-length from anterior margin of test lyrifera. 



Test more or less globular; apical system anterior; margin of labrum less than 



.20 test-length from anterior margin of test alta. 



Test sloping posteriorly; periproct oblique, plainly visible from above; petals I and 



V about as long as II and IV columbaris. 



Posterior petals more or less parallel or merged proximally. 



Posterior petals parallel, close together, not curving outward distally parallela. 



Posterior petals near together proximally but curving outward distally. 



Petals very large; petaloid area covering most of abactinal surface; its length 



is .70-90 test-length and its width .75-90 of its own length pacifica. 



Petals smaller; petaloid area about .66 test-length or less. 



First ambulacral plate in subanal fasciole is no. 7; 5 ambulacral plates 



included in subanal plastron; anterior petals directly diverging . . . elongata. 

 First ambulacral plate in subanal fasciole is no. 6; anterior petals ascend- 

 ing. 



Posterior end of test markedly oblique so periproct is more or less 



dorsal atlantica. 



Posterior end of test usually truncate so periproct is scarcely visible 

 from above luzonica. 



Brissopsis lyrifera. 



Brissus lyrifer Forbes, 1841. British Starfishes, p. 187. 



Brissopsis lyrifera Agassiz and Desor, 1847. Ann. Sci. Nat. Zool., (3), 8, p. 14. 



The geographical range of this well-known species is remarkable, extend- 

 ing as it does from Denmark Strait and southern Iceland through the seas of 

 northern and western Europe into the Mediterranean, and though apparently 



