216 Proceedings of the Royal Physieal Society. 



the anterior margin of the ventral portion of the body- 

 cnirass ; to it posteriorly are articulated the anterior ventro- 

 lateral and the anterior median plates. This part of the 

 bone was known to Pander, and is represented in two of his 

 figures (6, pi. ii., fig. 2, and pi. v., fig. 1, x), though in the 

 text he compared it with the jugular plate in Polypterus or 

 Osteolepis. Huxley, on the other hand (8, p. 35, fig. 21, a), 

 considered the bone to be hyoidean in its nature, as we have 

 already noticed. 



ISTeither Pander nor Huxley seems to have recognised the 

 lateral portion of this bone, which serves to articulate the 

 dorso-lateral portion of the cuirass with the ventral ; indeed, 

 Huxley remarks (8, p. 32) that " the ventral shield appears 

 to me to liave had no connection with the dorsal." But of 

 the connection of the two in the manner I have described 

 there cannot be the slightest doubt. See also my figure of 

 the parts in C. minor (13, pi. iii., fig. 3). 



The plates forming the expanse of the ventral shield are 

 already so well known from the figures of Pander and Hugh 

 Miller, that I need hardly enter into detail regarding them, 

 especially as I have in PL XL, Fig. 3, accurately given their 

 respective shape and mode of overlap. They are six m 

 number : — anterior median ventral (a. m.. v.), posterior median 

 ventral (p. m. v.), two anterior ventro-laterals (a. v. I.), and 

 two p>osterior ventro-laierals {p. v. I.). I may, however, 

 mention that, judging from the course of the lateral-line 

 groove on the anterior ventro-lateral plate, Pander has 

 reversed its position, putting the front end behind and vice 

 versa; for we shall presently see that on this plate the 

 sensory canal occurs on the anterior and not on the posterior 

 part of its surface. 



Distribution of the Lateral-line Grooves. — The course of 

 the lateral sensory canal is indicated on certain of the 

 dermal bones by conspicuous grooves, which, as in the case 

 of Fterichthys and Bothriolepis, have often been mistaken for 

 sutures. Tliere is, however, no difficulty in distinguishing 

 them irom sutures, when one by experience really comes to 

 know the characteristic appearance of the latter. 



On the anterior half of each anterior ventro-lateral plate is 



