TURBINARLE BIFRONTALES. 69 



Group VIII.— TURBINARIJ: BIFRONTALES. 



TurUrmrmns in which the margin of the cup /mm veriical folds, which fv^e hack to hack ; the subsequent 

 growth of the stock is earned on by these folds, which thus form froruis with calides on both sides. 



Species 5:j. Turbinaria bifrons. (PI. XXI. ; PI. XXXIII. fig. 1.) 

 Turbinaria bifrons, Bruggemann, Aim. and Mag. Nat. Hist., xix. (1877) p. 415. 



Description.— Cox&Vi.\im " consists of thin, vertical, variously pUcate plates," with calicles 

 on both sides. The Uve zone narrow, 4-5 cm. The suture along the ridge traceable here and 

 there, but much obscured. 



Calicles close but not crowded, arranged " quincunciaUy (the obUque series being more 

 pronounced), distant by about the length of their diameter." Lower margin slightly projects 

 ing so that the aperture faces upwards and outwards. Apertures oval, often oblong, less than 

 2 mm. long diameter. Septa 18-20, not thin lamelhe, but thick and granular, seen from above 

 projecting to the half-radius circle, in reaUty sloping straight inwards from the margm till 

 near the columella, where they dip down verticaUy round it to form a regular oval fossa at 

 the bottom of the funnel formed by the upper portion of the septa. Columella protuberant, 

 very compact and glassy. 



Interseptal locuU narrow jagged slits, not marked off peripheraUy from the furrows 



of the ccenenchyma. 



Ca'nenchyma shows a very beautiful and delicate ridge-and-furrow system, the ridges 

 being surmounted by single or double rows of fine granules, spines or spinous plates, the last 

 named being arranged transversely across the ridges. 



Briiggemann described this type from a portion of an old stock, which had lost all 

 traces of the early cup form. Its habitat is unfortunately not known. 



Among the many small cup-shaped young in the National Collection of Turbmanans 

 which show traces of the bifroutal foldhig, is a group from West Australia which seems to 

 form a transition series between this type and the next. Many of the smaller specimens of 

 this group show unmistakalile affinities in the characters of the calicles and of the 

 ca-nenchyma to the type of this species, while some of the larger specimens appear more 

 like T. conspima in these points ; and yet it does not seem possible to divide them. They 

 have many cliaracteristics in common, perhaps the more startling is the very early formation 

 of the bifrontal folds. There are specimens only 7 cm. in diameter which have lost all traces 

 of their cup shape, except the stalk, and are a mass of shallow fronds. It is possible that 

 these are all the young stages of a new type ; without, however, the complete series showing 

 the method of growth from the young to the old stock, it is impossible to do more than 

 speculate on this point (PI. XXL, two small specimens together). 



Provisionally, then, I propose to classify these small specimens as early stages of 

 T. hifron-s, in sjiite of the resemblance of some of them in certain points to T. conspicua. My 

 chief reasons for not including any of these under this latter type are : (1) they appear to 



