THE FAUNA OF THE ST. JOHN GEOUP. 137 



Thorax e segmentis cir citer xv, pleura breviores, et sulcata: apidbus rottcndatis. 



Abdomen parvum latitudine extensum, racM segmentis iii, costisque, etc. 



It may be remarked that neither the movable rheeks, the thorax, nor the pygidium 

 of L. aculeatus, as represented by the forms described by Gr. Liunarsson, appear to have 

 been recovered ; but from the close resemblance of the centre piece of the head-shield with 

 that of L. Oumigondiamis, we may anticipate that they will be found to correspond to the 

 description above given, which covers the characters of the two Acadian species. If, on 

 the other hand, the type of Angelin's species should prove to have the characters specified 

 by Dr. Brogger as those of Liostracus, then the two Acadian species will form a new 

 genus, of which Conocephalites tener, Hartt, will be the most characteristic type. ' 



LlOSTKACUS TENEB, (PI. I, figs. 3 a to c.) 



Conocephalites tener, Hartt, 1868 and 1884. Acad. Geol. 2ud éd., p. 652. 



C.neglectus, 



Plychoparia tener, Walcott, 1884. U. S. Geol. Surv. Bull. 10, p. 41. 



The body is elongate-ovate, except that the movable cheeks project in an arched 

 lobe on each side beyond the general contour. 



The features of the head-shield, so far as they concern its middle piece, were minutely 

 described by Professor Hartt, but he was not acquainted with the other parts of the body. 



The whole head-shield, including the movable cheeks, is narrowly subsemicircular 

 and was bounded by parabolic curves on each side ; the posterior margin projects back- 

 ward on each side so that the posterior edge of the movable cheek is opposite to the 

 aculeate end of the occipital ring. There are four pairs of furrows on the glabella, of 

 which the posterior originates opposite the eyelobe, and extends backward at a sharp 

 angle towards the base of the glabella ; the three anterior are very short and are grouped 

 opposite the anterior end of the ridge on the fixed cheek. The glabellar furrows are 

 plainly discernible only on the mould of the inner surface of the head-shield. 



The movable cheek is bounded outside by a parabolic curve, and is traversed through 

 the middle by a sharp, elevated ridge, which originates at the facial suture in front and 

 extends backward until it comes opposite the outward curve of the posterior extension of 

 the facial suture ; here it is met by a faint depression, corresponding to the posterior 

 furrow of the centre piece of the head-shield ; at this point, the end of the cheek turns in- 

 ward, forming a weak, flexible lappet, which extends behind the posterior margin of the 

 middle piece of the shield. Outside of the sharp elevated ridge, the margin of the cheek 

 is traversed lengthwise by about three distinct raised lines. 



The thorax has fifteen segments. The rachis is prominent and each ring has a 

 strong, broad channel, or groove, along the middle, and is elevated behind, where it over- 

 laps its successor. The pleurae are short, being only from a fifth to a third longer than 

 the width of the rachis ; they are curved backward in the inner half, but forward and 



' The form which Dr. Brogger found at Krekhng, in Norway, and referred to L. aculeatus, Ang., if one may 

 judge from tlie species associated with it, is not from so old a set of beds as the two Acadian species, but is of the 

 age of the Menevian fauna of Wales, or Band d of Div. 1. of the St. John group, whereas L. Ouangondiamis belongs 

 to Band c. 



Sec. iv, 1887. 18. 



