DavidRoyHunter.pdf

latest Tremadocian. Previously (Lindstroll, 19~5a), "conttod".. arcu"tus
s.f. and A.
reclinatu, s.f. were reporud fro," middle Arenigian sections
whiChahoYielded~,butthe)'occ"rredins .....llnu..hers.
~ •. f.prelu"",ablyevOlvedfrom~6.f·1
duringth.. ",arlyArenl11.lan.~s.f.,~•. f.andfo"",
transltionalbetweenthe"etwOwerereCoveredfrO"lh,,~LilOl!-
.tone, of
the Parohtodus origlnal!a Zone. on IIornhol... Denmark. (5. Stouse.
pers. COlOm.). Similarly, 101'1...... fonns WHe reported from the LIMV!rnbn
ofSwedll.n
(Fahneus, 1'166).
The evolutionary trend, frolll an
apparatus comprising exclud"ely
non-costate forms to an apparatus with costau and non-costat.. formS, app..arll
to " .."e culmInAted in th" Middle Ordovldll.n with an apparatus co''·
prlsing coacste: forlaS only.
It Is conc"-Ivable that apparatuS"s with costate
and non-coStste fOnls a~d
be .-"r.H.-ed to new genera respectively.
apparatus"" ..Ith only costate foru should
DREI'AtlODU5 ROBUSTUS (lI..ddinS, 19lJ)
2. figs. ~-12; Pt". 13. figs. 9,1.0; Fig.
DZIKI976. p. 400. Fill.. 11d,C,lt, not !.
Descrlptlon.~haSSycne[rica1ornearl)'s)' ....... trll'alb~co.-
tate dr"panodlfonllS, symmetrical l"ult1costat" drepanodifor..s, as)'....etric
bicoetate dr~panod1fonlle, w,,-altly blcostate uywaetrical drepaood1!on,,.
and costat", ohtodifo1"1lls.
The ey_etrlcalornearlysy-.tr1cal blcosta~e drepanodlfonu
have a robuetrecu,"""dcusp"that,:I.s anteriorly sharp andpoilter10.-11
.~ .-