tissue to the medial surface of the articular just in front 

 of and above the concave articular facet of that bone. 



Angular. — A small wedge of bone articulated by 

 interdigitation dorsally with the articular and anteriorly 

 with the dentary. Posteriorly the angular connects by 

 ligament with the interoperculum. 



BRANCHIAL APPARATUS. 



Hyoid Arch, Branchiostegal Rays, and Urohyal. 



Hypohyals. —Both hypohyal elements well de- 

 veloped, and of about equal size; the dorsal element 

 cartilage filled at its ventral and posterior edges, the ven- 

 tral element cartilage filled at its dorsal edge; the two 

 elements articulate with one another through the car- 

 tilage that lies between them; the dorsal and ventral 

 elements articulate by fibrous tissue at their antero- 

 medial edges with their opposite members. The dorsal 

 hypohyal articulates posteromedially by fibrous tissue 

 with the lateral surface of the first basibranchial. The 

 posterior edge of the ventral hypohyal and a short portion 

 of the posteroventral edge of the dorsal hypohyal articu- 

 late through cartilage and fibrous tissue with the 

 ceratohyal, while the medial surface of the ventral 

 hypohyal is held by fibrous tissue to the anterodorsal 

 region of the urohyal. 



Ceratohyal. — A flat shaft, wider posteriorly than 

 anteriorly; cartilage filled at its lower posterior edge; ar- 

 ticulates through cartilage anteriorly with the ventral 

 hypohyal and, to a lesser extent, with the dorsal 

 hypohyal; articulates posteriorly through cartilage and 

 interdigitation with the epihyal. K six branchiostegal 

 rays are present, the first two rays articulate in about the 

 middle or just behind the middle of the ventral edge of 

 the ceratohyal. However, only five branchiostegal rays 

 are usually present and only one articulates to the ven- 

 tral edge of the ceratohyal. Of the four branchiostegal 

 rays always present in the posterior group, the lower two 

 or even three have their fibrous tissue articulation 

 primarily with the lateral surface of the posterior end of 

 the ceratohyal in the region immediately below the inter- 

 digitation with the epihyal. 



Epihyal. — Large, about the same size as each of the 

 hypohyals; cartilage filled at its ventral edge; articu- 

 lates through cartilage and interdigitation anteriorly 

 with the ceratohyal, while dorsally it articulates by 

 fibrous tissue with the interhyal and interoperculum. 



Interhyal.— A short, thick rod; cartilage filled at 

 both ends; articulates by fibrous tissue ventrally with the 

 epihyal and dorsally with the extreme posterior end of 

 the symplectic and the ventral edge of the metapterygoid 

 just behind the symplectic. 



Branchiostegal rays. — Usually five in number. Of 



the 12 specimens examined, 11 have five branchios- 

 tegals on each side, one articulated to the middle of the 

 ventral surface of the ceratohyal and four articulated to 

 the lateral surfaces of the posterior and ventral ends of, 

 respectively, the ceratohyal and epihyal. However, one 

 specimen has five branchiostegals on one side and six on 

 the other. The side with the five branchiostegals has a 

 typical arrangement of one ray articulated to the ventral 

 surface of the ceratohyal and four articulated to the 

 lateral surface of the ceratohyal and epihyal. On the one 

 side with six branchiostegals, two are articulated to the 

 ventral surface of the ceratohyal and the other four more 

 posteriorly. In the illustration of the branchial apparatus 

 of M. ciliatus. the additional branchiostegal ray occa- 

 sionally present is indicated by dashed lines, this being 

 the branchiostegal ray immediately behind the large 

 first branchiostegal articulated to the ventral surface 

 of the ceratohyal. The branchiostegal rays are all 

 articulated by fibrous tissue to the ceratohyal or epihyal. 

 The first branchiostegal is much wider than are the 

 succeeding rays, the more posterior of which are so 

 narrow that they are, in essence, slender rods. 



Urohyal. — Thick along its anterior and anterodor- 

 sal edges, otherwise a relatively thin plate; articulates by 

 fibrous tissue anterodorsally between the medial edges of 

 the ventral hypohyal, while posteriorly it articulates with 

 the ventral surfaces of the posterior end of the first 

 basibranchial and the anterior end of the second 

 basibranchial. 



Branchial Arches.— All the elements are cartilage 

 filled at their edges of articulation with the other 

 elements of the series, and the articulations are usually 

 through cartilage and fibrous tissue. The branchial 

 arches are composed of three basibranchials, three pairs 

 of hypobranchials, five pairs of ceratobranchials, four 

 pairs of epibranchials, and two pairs of pharyngo- 

 branchials. Four gills are present, with a slit between the 

 fourth arch and the lower pharyngeal. 



First arch.— Basi-, hypo-, cerato-, and epibran- 

 chial elements present. First basibranchial short, wider 

 posteriorly than anteriorly; articulates posteriorly with 

 the second basibranchial and posterolaterally with the 

 first hypobranchial. First hypobranchial of increasing 

 width posterodorsally; the largest of the hypobranchial 

 elements, which decrease in size posteriorly in the series; 

 articulates ventrally with the region of articulation 

 between the first and second basibranchials and dorsally 

 with the first ceratobranchial. First ceratobranchial a 

 stout rod; the longest of the ceratobranchial elements, 

 which decrease in length posteriorly in the series; no ven- 

 trally directed flange present on the ceratobranchials, ex- 

 cept for the fourth, which is somewhat compressed and 

 has a small ventral flange basally; articulates ventrally 

 with the first hypobranchial and dorsally with the first 

 epibranchial. First epibranchial a flattened plate, 

 rounded ventrally where it articulates with the cerato- 



