KONGL. 8V. VET. AKADEMIENS HANDLINGAR. HAND 34. S;0 8. 7 



the latera] margins and may be designated as the anterior groove and the posterior groove. 

 Beside these grooves there are in some instances others, '»ne on each of the latera] mar 

 gins, parallel with these. < m both sides of the anterior margin a protuberance, sometim.es 

 of considerable length, stånds out. They are benl backwarda towarde the interiör side <>f the 

 hypostoma and in some genera, as Dysplanus, assume the shape of long, accuminated, 

 halfways hollow horns. These protuberances were called ailes* \>\ Barrande and it i- 

 best to retain this term, in ent»lish »wings , in spite of its being no1 quite expressive. A 

 smaller posterior pair lies nearer to the posterior margin and these wings are so mucb 

 bent backwards, that they are seldom visible from the outside. They are prolongatione 

 from the »duplicature» or the narrow fold of the posterior margins round the interiör 

 side of the hypostoma. 



For the rest the whole exteriör surface is covered with terrace lines running eon- 

 centrieally and varying according to the differenl genera and even species. Many other 

 genera, again, as Acidaspis, Calymmene, llomalonotns, Dalmanites etc., are devoid of them 

 and instead granulated or smooth. 



In the plurality of species there are two tiny patches or maeuhe, sometimes ele* 

 vated above the surrounding surface like tubercles and so they have also been called by 

 some authors. But I have prefered to use the name »macula» for them, as the plura- 

 lity does not form tubercles. They are generally entirely smooth and glossy and situated 

 next to the anterior groove, either above it or in it, at a regular distance from each 

 other and the Latera] margins. They may form a stink spöt or, as comraonly, an ovoid 

 or elliptic area surrounded by a linear elevated börder. Thus amongst the Asaphidse. 

 In others, again, (Bronteas, llhenus etc.) they form a moderately elevated tubercle. The 

 direction in which they are oriented in relation to the longitudinal axis of the hypo- 

 stoma is quite as variable. It is to the closer consideration of the nature of these ma- 

 culae that this memoir will be chiefly devoted. They have been delineated severa] tinies, 

 but very seldom lias any accurate attention been paid to them by previous authors. It is 

 higlily doubtful if Barrande ever alluded to them, when he in his »Systéme Silurien de 

 Bohéme» vol. I, p. 156, in describing the hypostoma, says: »Cette plaque bombée porte 

 souvent des saillies et des empreintes creuses, dans le voisinage de la bouche. Leurs 

 formes varient suivant les espéces mais en conservant toujours les caractéres génériques. 

 Notis les considérons comme les points d ? attaches des muscles et des måchoires.» In the 

 numerous speeific descriptions in his grand work there is never any mention made of 

 the maculae and in contemplating the tigures and reading the explanations of these, vve 

 shall lind that he meant something more compreliensive with his statement, to wit, the 

 entire groove where these tubercular maeuhe are situated. 



In Novåk's third paper, p. 4, wc see the figures of two Phillipsiae w ith tubercles 

 on the hypostoma and he says only that in the anterior groove there are two such sym- 

 metrically placed . . . glandular intumescences. l 



Brögger again in his paper on the »Ausbildung des Hypostoms» devotes a page 

 (p. 19) to explain the nature of these maculas and regards them as the exteriör marks- 



1 »In der Mittelfurche sitzen 2 kleine symmotrisch gelegene, nicht immer dcutliche drusenartigc An 

 .schwellungen.» 



