S4 G, P. MATTHEW ON THE 



Angeliu seems to have thought this genus au important one, as he made it the type 

 of a family, LeptojAaslidce, in which he included Olenus, Parabolina, Peltura, Acerocare, 

 Eurycare and Sphœrophthalmus. Leptoplastus was probably regarded by him as a link 

 between the first four of these genera and the two last, and thus most suitable for the 

 family type. "Within the genus there are species that ally it to Olenus and Peltura on 

 the one hand, and to Sphaerophthalmus and Eurycare on the other. 



The most obvious distinction between Leptoplastus and Olenus is in the position of 

 the eyes, which in the latter genus are in advance of their normal position in trilobites. 

 There are other differences, as the number of segments in the thorax, form of pygidium, 

 etc., not easy of recognition when the trilobites are dismembered. 



In Leptoplastus the head is more strongly vaulted than in Olenus and its allies, and 

 the genal spines more flaring. Dr. Brogger has thought it advisable to assemble the 

 vaulted species under Leptoplastus as a generic name, making Eurycare, Spheerophthal- 

 mus and Ctenopyge subgenera, thus recognizing the value of Leptoplastus as a centre for 

 this group of forms. 



Angelin's description of Leptoplastus was as follows : 



Corpus oblongatum vel ovatum, distincte longitudinaliter trilobum, crusta Isevissimum 

 prœditum. 



Caput semilunare, undique anguste marginatum, sulcoque intramarginali ; auguli 

 exteriores spinis brevibus armatis. Oculi modici, semilunares distantes, centrales, lobi 

 orbitali prœditi. Costfe faciales obliquœ. Frons breviuscula, ovata, sulcum marginalem 

 hand attingens. 



Thorax segmentis 11-12 longitudinaliter sulcatis, apice accuminatis. 



Abdomen parvum, margine armatum vel muticum ; rachis distincta, marginem sub- 

 attingens.' 



Leptoplastus latus, Matt. (PI. XIII, figs. 10 a-c.) 



Leptoplastus latus, n. sp. ' Can- Rec. Sci.,' 1891, p. 462, figs. 1, 2 and 3. 



Body without the movable cheeks, suboval. Crust smooth. 



Head strongly arched downward in front, and (including the movable cheeks) about 

 four times as wide as long. Centre-piece of the head subtrapezoidal in outline ; anterior 

 margin straight, having a fine thread-like fold. Grlabella prominent, short, cylindrical, 

 broadly rounded in front, reaching the marginal furrow ; there are two pairs of furrows, 

 very faint, arching backward from the sides of the glabella and extending about one-third 

 across ; occipital furrow distinct, extending all across ; occipital ring rounded, and 

 rounded forward at the ends ; it bears a small median tubercle. Fixed cheek broad, tumid, 

 crossed obliquely one-third from the front by a faint ocular fillet ; eyelobes prominent, 

 broadly ovate ; posterior marginal fold very faint, and rounded forward to the eyelobe. 

 Movable cheek tumid, rudely lozenge-shaped, broadly rounded on the outside, and 



' Body oblong or ovate, distinctly three-lobed lengthwise, with a very smooth crust. 



J/cad semicircular, narrowly margined all around, and having a groove within the margin; exterior angles 

 armed with short spines. Eyes of moderate size, semicircular, distant, central, furnished with orbital lobes. 

 Facial ridges [ocular fillets ?] oblique. Glabella rather short, ovate, scarcely reaching the [anterior] margin. 



Thorax of 11-12 segments, grooved lengthwise, and having the apex acuminate. 



Pygidium small, spined, or smooth on the margin ; rachis distinct, scarcely reaching the margin. 



