86 SYSTEMATIC ARRANGEMENT 



j_ — Species without spines a)id tubercles. Trimerus, Green ; Homalonotus, König. 



2. H. Knightii: Scuto caudie acuminato, annulis rhachis 8-9, costis lateralibus 6. Long. corp. 3-4". 

 Re/.—Kö'üiG, Icones Sectil. i, 4, Plate VII, Fig. 85. Bronn, Letltaa. i, 119. 107, Table 



IX, Fig. 14. MuRCHis. Sil. Syst. n, 651, Plate VII, Figs. 1, 2. Milne Edw. 



Cr. iii, 315. Homalon. Z?<6?raOT5, Murch. ibid. Figs. 3, 4. Emmr. i)me?-;'. 41. 8. 



Bronn, Leonh. Jahrb. 1840, 445. 

 Found in the grauwacke strata of the Eifel at Daun (according to specimens in Sack's 

 collection), and in the upper Silurian strata of England. 



I have examined only two caudal shields of this species ; they are comparatively shorter 

 and broader than that of the following species, the axis is more flatly arched, and more dis- 

 tinctly pointed at the end, owing to a furrow which surrounds it. We can recognize in it 

 seven distinct rings, besides the margin of articulation ; there is also an eighth, and indeed, 

 even a ninth ring, but very slightly marked ; after which follows the short triangular pointed 

 extremity. There are six strong broad ribs on the sides. The point of the shield is broken 

 off in the specimen, but it must have been prominent. 



3. H. delphinocephalus : Scuto caudse acuminate, in apice reflexo, annulis rliachis 11-12, costis 

 lateralibus 8. Long. corp. 3-6". 



Bef. — Trim, delph. Green, Mon. 82, Fig. 1 (Model, No. 32). Emmr. Dissert. 41. 7. 

 Bronn, Lethcea, i, 112. 100, Table IX, Fig. 5. Homalon. delphino-cephalus, Murch. 

 Sil. Si/st. ii, 651, Plate VII, to Figs. 1, 2. Milne Edw. Crust, iii, 314. 1. Homalo. 

 Ahrendi, RoMER. Verst. des Harzes, 39. 1, Tab. XI, Fig. 5. 



Found in a yellow grauwacke from the Eifel, containing a considerable quantity of iron 

 (according to specimens in Sack's collection) ; also in the transition limestone of North 

 America (Williams ville, Niagara, New York), and of England (Wenlock, Dudley). 



The rich collection of Mr. Sack contains perhaps a dozen caudal shields of different size 

 (varying from half an inch to two inches in length), besides fragments of all parts of the 

 head, and some joints of the body, all belonging to this species. They correspond in the 

 principal points with Murchison's very accurate figure. The caudal shield, which appears 

 to me to present the best specific character, is comparatively shorter, more acutely triangular, 

 very prominently pointed at the end, and is here rather flatly extended. The axis is 

 certainly more convex, but not so strictly defined as in the preceding species ; its rings are 

 decidedly shorter but higher, and separately, with a much sharper edge. I have counted 

 eleven distinct rings, and a very indistinct twelfth ring, besides the margin of articulation ; 

 eight equally distinct ribs are perceptible on the sides, which are situated less towards the 

 external part, and more posteriorly. 



