76 W. M. Bale: 



as seen in the other aspect the sides are less convergent down to the 

 tloor or diaphragm, hehjw ^\hich they curve inward, making the- 

 outline hell-shaped. Tlie thickening of the calycle-wall may he 

 quite pronounced in the broader view, while not appearing in the 

 narrower aspect. This thickening is generally greatest at the 

 margin of the liydrotheca. becoming gradually less towards the 

 diaphragm. The conspicuous inwai'd thickening which forms the 

 diaphragm is pierced by a central channel, or hydropore, w^hich 

 expands into a small rounded cavity between the diaphragm and 

 the base of the hydidtheca. If the same liydrotheca be viewed in 

 its narrow aspect tlie sides will appear (|uite tliin, and even at the- 

 base tlie perisarc will not appear very thick, as the central enlarge- 

 ment of the hyd)'opore appears in this view to nearly fill the space 

 lielow the diaphraiini. But in some colonies all the hydrothecae 

 may appear thin-walh'd. in whatever dii^ection they are viewed. 



Sometimes the border of the liydrotheca may be a little everted, 

 in •)ther cases not at all. especially when thick at the margin. 

 Considerable differences in size often exist among the hydrothecae- 

 of a single colony. I have not detected any sign of bilateral 

 synnuetry in the hydianths. which have a very large hypostome and 

 from about 24 to '50 tentacles. The peduncles may be of any length, 

 fnim twice that of tiie hydrothecae to twenty times, or even more. 

 Tliey are thin-walled, and twisted in a loose irregulai- spiral, with 

 oreasionally smooth interspaces. 



The typical g(uiangia are oblong or ovate, tapering below, smooth, 

 and when matuie rounded at the top. They are but slightly com- 

 piessed. But variations fi'om the type are abundant ; sometimes 

 there are two intlatiojis. corresponding to the two contained zooids, 

 in other cases tliere ai-e still more irregular forms, and there may 

 be a series of annular undulations., Agassiz describes the goiiothecae 

 as about twice the length of the hydrothecae; in my specimens I find 

 them three to foui- times as long. 



Miich difference of opinion exists as to whether O. cal/riilafa and' 

 ('. i/i/ei/ra aj'e the sanie species. Among those wlio support this 

 view are Levinseii. iliiula. Billai-d. and Linko. while Hartlaub, 

 Calkins, and Nutting hold the contrary oj)iTiion. 1 am a1 the- 

 disadvantage of not having seen Birula's pa]>er, but I fiml fi-om 

 ]Jid\o that ('. i/if('(/ro. forma fi/p/ca, is distinguished hf its orbicu- 

 lai- and thin-walled liydi'otliecae from forifur ral/ciilafn, in which the 

 liydi-.ithecae are cdmiiressed. with thick walls. This distinction 

 obviously does not iiuld good, since we find the compressed hydro- 



