OF THE SPECIES. 67 



groove before the lateral margin, which ini])rcssion is continued posteriorly, and returns into 

 itself at the posterior margin of the cephalic shield ; the external border is slightly convex, 

 and produced at the posterior part in a long slightly incurved spine. 



Body many-jointed, apparently only having a definite number of joints in tlie separate 

 species (16-20), the joints towards the posterior part gradually more narrow and shorter, 

 the lateral lobes at first produced diagonally, and in this part almost as broad as the rings 

 of the body ; afterwards projecting in a long angle turned outwards and backwards ; a deep 

 diagonal impression on the transverse portion, which extends from the most anterior and 

 innermost angle backwards, to the origin of the spine. 



Caudal shield circular or oval, without (?) lateral lobes and enlarged sides at the base, 

 with a short but articulated axis, and a flat border to the posterior portion. 



Localitij. — In the oldest Palaeozoic strata (grauwacke, clayslate, and alumslate) ; 

 hitherto only found in Bohemia, Sweden, and near St. Petersburg. 



Remark. — I know onlj' two distinct species of this genus from my own observation, and confine 

 myself here to the description of these two, but in so doing would not be understood to question the 

 propriet}'' of tlie others to rank as species. Naturalists having an opportunity to investigate perfect 

 specimens of the species which I have not admitted, will be able to decide how far they really differ 

 from the two here enumerated. 



1. P. Eohemictis : Protuberantia capitis clavata ; anguUs scuti cephalici dimidio corpore longi- 

 oribus ; trunco \acies annulate. Long. 1-6." 



Vur. juveii: annulis trunci 18; lobo lateral! secundo in spinam longissimam extenso. Tab. I, Fig. 6. 



Ref. — Oleiiiis pi/mmidaUs, Zenker, Beifr. etc. 41. Tab. IV, Fig. T. U. V. Tril. gracilis, 

 BoECK, Magaz. f. Naturw. I, Fig. 15. Sternberg, Verh. d. Vaterl. Mm. 1825, 

 Tab. I, Fig. 4, C, and 1833, p. 47. 

 yEfafe paulo provectiorQ) Tril. minor Boeck, 1. c. f. 12, 14. 

 Var. senilis: annulis trunci 30; lobo lateral! secundo reliquis aequali. Tab. I, Fig. 5. 

 Tril. bohemicus, Boeck,/. c.f. 2. Sternberg,/, c. 1825, 83. Tab. I, Fig. 4. A. B. 1833. 

 46. KiNSKY, \nBoriis Abha7icll. etc. I, 246, Fig. 4, 5, 7. ?'. longicandatus, Zenker, 

 Beifr. 37, Tab. 5, Fig. A to F. Emmr. Diss. 48. 4. Milne Edw. Cnist. iii, 

 341. 2. Olenus Tessini, Var. 1. Dalm. Palaad. 73. 

 Central part of the cephalic shield rather quadrate, but the distance between the 

 eye-plates rather greater than the longitudinal diameter ; the anterior round lobe of the 

 glabella longer than the three others together. Spines of the maxillary shield longer than 

 half the body ; the spine of the second ring of the body as long as this during the youth of 

 the animal, gradually getting shorter, and finally reduced to the same length as the spines 

 of the other body-rings. Rings of the body less numerous during youth (sometimes sixteen, 

 usually eighteen), at a more mature age probably always twenty (at least I have never seen 

 a greater number in perfect specimens). Caudal shield quite oval, rather broader towards 

 the posterior part, almost flattened, the axis inarticulated during youth, afterwards one- 

 jointed, at maturity furnished with five joints. 



Locality. — In a blackish-green grauwacke of Bohemia, near Horrowic and Ginec ; also in 

 Norway and Sweden, in the latter in alumslate, at Olstrog, Dämmen and Carlsfors. 



Remarks. — 1. 01. pyramidalis, Zenker {Tril. gracilis, Boeck) I can only agree with Count Sternberg 

 in regarding as a young specimen of the Tr. lonyicavdufus and Tr. bohemicus of the same author, and 



