SUB-CLASS i HYDROZOA GRAPTOLITOIDEA 1 1 9 



moiioprionidian branches, which originate from ;is many subdivisions of tin; 

 funicle ; tin- latter often enveloped in a central corneous disk. Ordovician. 



Dicr<in<>'ir"i>tn<, I lall ( Fig. '2 1 1). Hydrosoma composed of two symmet rically 

 d. -veloped branches which arr coalcseent in the proximal, and free in the distal 

 portion of their length. Distal end- of hydrot hecar isolated and incurved. 

 Ordovician. 



Sub Order B. DIPRIONIDAE. Hopkinson. 



iHJ "f /"'" "/' '//""/' /' /7/W fOWt "/' /' '/'//'"/A' <'"< jtfii,;,/ 1,,,,-J; I,, 

 Inn-/:, tritit tin' rir<lill<i< /vwA'.sr///,/ f /"''lit " lit ml 



/>/l>/!/i-<t/>fn.<, M'Coy (Fi^. L' 1 -'5, </, /). Hydrosoma 

 lineai', diprionidian. Hydrothecae rectangular in 

 section, inclined, directly overlapping. Vii-gula em- 

 ledded in a median septum, commonly projecting 

 distallv as a long n'bre, and appearing proximally as 

 a radiele. Primordial buds originating along whole 

 length of sicular margins. Ordovician and Silurian. 



('/iiiKii'iiifi-n/ifii.'i, Hall (Fig. iM:5, u, c). Like the 

 preceding, luit with hydrothecae separated and stand- 

 ing nearly vertically ; they are furthermore sub-oval in 

 section, and distally somewhat .contracted. Ordovician 

 and Silurian. 



PhyUograptos, Hall (Fig. 214). Hydrosoma leaf- KI.:. 214. 



like, and composed of four uniserial rows of prismatic /'>< V'".-" /''"- t"i- 

 hvch-othecae coalescing along the whole length of their Poi n t I>^B, <Sda. a.sSwai 

 dorsal margins. Hydrothecae often with two lateral f}5gJ i S^^ c e ti 1 Sj u ; 

 apertural spines. Base of the Ordovician. (p*r Hail). 



Sub-Order C. RETIOLITIDAE. Lapworth. 



rk of t/i<' i-nnmum nmnl iiirinif nrii/in in ii Ins>'fi'i1 pn/>/j>trr>/. rift/it/" 

 <iin/</<' mid rmfi-nl, nr i/tiji/ii-<i/i' "//'/ nffiir/n-i/ to opposite si'lex <>f flic jieri'/t / in : 



tin' lilffrr i..< 111 licit iiftt'iniufnl, unit tilji/mrt,;/ H/xni ,i iK'tir,,,']; i,f dlitlHOUS fibt'CS. ^i''H/" 



absent. 



Ufa, llai-r. (Fig. 215). Hydrosoma undivided, elongate, compressed, and 

 tapering toward the extremities. Hydrothecae disposed in rows on each side 

 of the axis, inclined, and in contact with one another. Virgulae two in number, 

 separated, and attached to opposite sides of the peridermal network in the 

 median plane of the hydrosoma ; one is rectilinear, the other zigzag-shaped. 

 Ordovician and Silurian. 



Sftomaiograptus, Holm; /.V/^/.v/y./y/s, Hall; /".'/''"/''"' Emmons. Or- 

 dovician. 



Range and Distribution of the Hydrozoa. 



Of the Hydio/oans in which preservation is at all possible, the 7/W/v-i*/W- 

 Unae are known with certainty as far back as the Upper Cretaceous. During 

 the Tertiary period they achieved a s..mewhat greater distribution, but have 



