]()9 DESCKIFIIOX OF THE HAKD PARTS OF SOME 



far from ?jeing so exceptional in its structure as has been generally 

 supposed, is structurally very intimately connected with Pycnopodia and 

 Crossaster. We might readily transform a Pycnopodia or a Crossaster 

 into a Brisinga by reducing the actinal and abactinal interbrachial spaces 

 into a minimum, which would give us a Starfish with a small disk, in 

 which the ambulacral plates adjoining the actinostome assume a great 

 development, and thus the numerous arms would appear quite discon- 

 nected (as in Brisinga). The connection of the arms in Starfishes does 

 not depend so much on the greater or less development of the ambu- 

 lacral and interambulacral systems, as upon the greater or less increase of 

 the limestone network forming the interbrachial spaces, which, although a 

 feature greatly affecting the physiognomy of the Starfish, yet influences 

 but slightly its internal structure. 



The range of this species is from Sitka to Mendocino City, California. In 

 the Gulf of Georgia and at Mendocino it is a very common species in shallow 

 water and at low-water mark. 



BEISINGA. 



The genus Brisinga, with its long slender arms, the whole actinal side 

 of whi(!h, with the exception of the large interambulacral plates forming 

 the edge of tlic arm, is occupied by the ambulacral plates, shows us very 

 distinctly how we can pass from the Starfish to the Ophiuran by the 

 joining of the large interambulacral plates on the lower surfiice, and their 

 becoming soldered together into one plate to form a lower arm-plate, so 

 that the absence of interambulacral plates, which has alw.ays been cited 

 as tlie great difference by which Starfishes and Ophiurans could alwaA-s 

 be distinguished, is readily explained ; the lower arm-plates of Ophiurans 

 being only modified interambulacral plates. We further find, on examin- 

 ing, in Brisinga, the secondary imbricating plates forming the arches 

 which support the abactinal membrane covering the arms, each of which 

 carries only a single spine, and is arranged in more or less regular 

 curves, that we have some approach already to the side arm-plates 

 so characteristic of Ophiurans, the separation of the so-called disk from 

 the arms, — which, although so striking a feature of the genus, is less im- 

 portant than it seems at first sight, — being merely brought about by the 

 reduction to a minimuin of the lateral spreading of the actinal part of 

 the secondary and interambulacral plates. In the case of Brisinga this 



