NO. 1152. CAMHRIAN liRACniOrODA—WAIMOTT. 395 



davisi or 0. {L.) amplus. The outside laterals (/, (i^s. 4, 5) are finely 

 preserved in O. (L.) darisi, as are also tlu^ IransiiuMliaii scars (/, fi^. 5). 



Tiic interior markinj;s show vascular sinuses in both valves (.v, IMate 

 XXVll, ligs. 1, 2, 4; Plate XX VI II, (igs. 2, 3, 4, 5, 0, 7) and a distinctly 

 marked visceral area (/') on tiie ventral valve. A eonsiderablii varia- 

 tion in tlie ontliiui and position of the. vascular sinuses and vis(;eral 

 areas occurs in the species illustrated on the plate, and important mod- 

 ilications oc(!ur in sevc^ral other species. 



A nairow mcdiiin ridj4e or sei)tuin is lre(iuently observable in the 

 dorsal valve (Plate XXVII, (i{,^ 4; Plate XXVIII, lij^s. 2, 4); but with 

 the exception of what may be considered as indicating its ])robable 

 l)resence in one specimen of a ventral valve of <>. {L.) davul (see I'late 

 XXVII, lig. 1), no traces of a sciptum hiiv(^ been observed in the \en 

 tral valve of any species referred to the genns. 



Type of subgenus, IAn<iuU'U<i davisi Me(!oy. 



Ohscrralions. — Wiien in Wales, in 1888, I made a, small collection of 

 <). {L.) davisi at the type locality at Port Madoc, and Liter Mr. (1. ,1. 

 Williams sent nui a number of fine sj)ecimena for study. All of the 

 nniterial was carefnlly ju'epiU'cd by I)i'. (Jeorge M. dirty, who made a 

 l)reliminiiry study ol" tlu^ tyi)e and other spe(;ies referred to the gcMius 

 when 8ui)erintending the preparation of the drawings. The systematic 

 study of all the spetMCS that have- been referied to lAtKinlcUa is now in 

 progress in conne(;tion with the study of a (!onsiderable amount of new 

 nniterial from various localities in the Cambrian rocks of North America. 



The vertical rang(5 of lAnguleUa is from tlu^ upper horizon of the 

 Olenellus or Lower (Jambrian fauna to the summit of the Cambrian 

 and into the Ordovician fauna. The old<\st known species is (). [L.) 

 (/rdnrillensis, which is asso(;iated with Olenellus in strata n^ferred to 

 the upper portion of the Olenellus zone. ^Phe greatirst deveJopirjent of 

 sp(M5ies is in the iMiddh; and Upper (3and)rian, only a few forms (;ontinu- 

 ing on into the Lower Ordovit^ian fauna. 



There are two other species of Obolus in the Lower Ordovician of 

 Newfoundland that will be I'nily illustrate-d in the general work u])on 

 Cambrian ISrachiopoda. They are Obolus {/An</nloholns) alfinis and 

 Oholus ( lAnguloholus) spuHUH. Mr. G. F. Matthew i)laced the two species 

 under distinc^t genera, JAnf/ulohohis (ijjinis and SjAuvrofiolus spissiis. 



The study of a considerable <iiuintity of material that I collected at 

 the typical locality on (Jreat IJelle Island leads to the conclusion that 

 hotli spe<;ies should be referred to tlu^ genus Oholns^ subg<Mins lAmju- 

 loholus, 181)5, the latter being the same as the subgenus of Oholiis [Thy- 

 sauotos) Mickwit/, 18<M), of which (>. (T.) miuricus Eichwald is the type. 



It is a curions and interesting fact that the ix'cnliarity of the area of 

 the dorsal valve, to which Mr. Matthew gives mneh imporlance, is 

 also i)resent in the oldest of the Oholits grouj), (>. {L.) (franvillciisis, and 

 in one or two other species in the Middle and lJ|)p(!r Cambrian. 



