1894.] SAiMOWOID FISHES OP THE ENGLISH CHALK. 659 



the exposed portion of the scale sometimes shows only the con- 

 centric lines of growth, sometimes is ornamented with very fine 

 closely-arranged radiating lines of tubercles. The latter ornamen- 

 tation is probably normal and varies \\ ith the state of abrasion of 

 the fossil. The scales of the lateral line are not enlarged ; the 

 course of the sensory canal is marked by a feeble ridge and a notch 

 in the hinder border of most of the scales. 



2. Elopopsis ceassus. (Plate XLIII. figs. 1, a-c.) 



Osmeroides crassus, F. Dixon, Geol. & Foss. Sussex, p. 376 

 (1850) ; A. S. Woodward, Proc. Geol. Assoc, vol. x. p. 322 (1888). 



The name of Osmeroides crassus was given by Dixon to a unique 

 specimen from the Chalk of vSussex now in the Brighton Museum, 

 but the fossil has hitherto been only briefly noticed without 

 detailed description. The Avriter has thus availed himself of the 

 kindness of Henry Willett, Esq., and the ex-Chairman of the 

 Museum Committee (Edward Crane, Esq.), to examine the original 

 specimen more closely. It comprises the head with the anterior 

 part of the abdominal region of a large fish, much fractured and 

 crushed and exhibiting part of the pectoral fin on the left side. 

 The right side of the head is represented in PI. XLIII. fig. 1 ; an 

 upper view of the ethmoidal region is given in fig. la ; and separate 

 drawings of the left premaxilla and dentary are given in figs. 1 b, c. 



The superficial bones exhibit no ornamentation, merely the lines 

 of growth and in places sensory canals. The cranial roof is much 

 crushed and fractured and thus too imperfect for description. The 

 great extent of the frontah, however, is well shown, and the much- 

 expanded and truncated ethmoid (fig. 1 «, eth.) is completely 

 preserved. The fostorlital plates (fig. 1, pi.o.) cover the cheek 

 between the orbit and the preoperculum, and there are also remains 

 of well-developed suborlitals (s.o.). The 2^''em<:uviUa (figs. 1, 1 b, 

 pmx.) is relatively small, elongate-triangular in shape, and furnished 

 on its oral margin with a close series of small conical teeth. 

 "Within the mouth, and apparently fixed on the same bone, are 

 also two much-enlarged teeth, laterally compressed but without 

 trenchant edges ; the foremost, placed at the anterior end of the 

 bone and shown only by the base, is the smaller of the two ; the 

 second, well-preserved on each side, occurs at about the middle of 

 the bone. In the fossil the anterior ends of the premaxillse are 

 widely separated, but this may be due to crushing. The maxilla 

 (fig. 1, mx.) is very large, extending back-n^ards beyond the orbit, 

 and overlapped above by either one or tAVO supramaxillary bones 

 {s.mx.'), which are too much crushed for description. The oral 

 margin of the bone is convexly arched, and in the fossil ciurves 

 slightly inwards ; it bears a single regular series of very short and 

 stout conical teeth, larger than the marginal teeth of the pre- 

 maxilla, and there are appearances of a second series of smaller teeth 

 occuring immediately within. The dentary bone of the mandible 

 (fig. 1 c) is deep behind and tapers rapidly to an almost pointed 

 symphysis ; it bears a single series of well-spaced, large, conical 



44* 



