178 PROF. W. K. PARKER ON THE STRUCTURE AND 
is about equal in size to the pharyngo-hyal; this segment possibly corresponds to the 
distinct symplectic of the Sturgeon and Paddle-fish’. 
The lower part of the hyoid arch is longer and broader than the large mandibular 
ramus (Pl. XXXVI. fig. 2, c.hy); its lower part is broken up into three small segments, 
equalling in average size the upper elements. 
This broad but solid rib of cartilage is arcuate ; in general form it is narrower above, 
and broader below, the top part (st.2) being both notched and rounded ; the broad lower 
part is emarginate, and has two lateral facets for the hypohyals (h.hy). 
There are two hypohyals (h.hy', h.hy*) attached to the supero-external angle of the 
great cornu; but these have become confluent (see in Menopoma, Pl. XXXIX.) ; 
together they form a thickish rod hooked inwards to join the median piece (b.hy), which 
has coalesced right and left with these small distal hypohyals (PLXXXVII. fig. 4, h.hy’). 
The third hypohyal (h.hy’) is a truncated oval, attached by its broad part to the 
infero-internal angle of the great cornu (c.hy). 
Outside the largest hypohyal there is another very small nucleus of cartilage on the 
left side. 
The ligaments connecting the parts at the angle of the mouth are well seen in this 
skull. The “suspensorio-stapedial ligament” has the pharyngo-hyal in its substance, 
and the “ hyo-suspensorial ” (/. s./) has the epihyal (¢./y) in its upper end; the “ mandi- 
bulo-hyal” (m. h./) runs upwards and backwards under the distal part of that ligament 
from the angle of the jaw, and is attached nearer the end of the styloid part of the 
ceratohyal. 
In Menobdranchus none of these ligaments have cartilage in their substance. 
The basihyal (4.hy), contrary to rule, sends a process backward towards the first basi- 
branchial ; it is pyriform, with the narrow end behind, and is confluent right and left 
with the small second hypohyals. 
The third and fourth branchial arches are not retained in this species; they are in 
Menopoma, and also ina small Japanese “ Cryptobranch,” viz. Onychodactylus (Trans. 
Linn. Soe. ser. 2, Zool. vol. ii. 1880, pl. xix.). 
The next basal element is roughly marked out into a first and second segment 
(Pl. XXXVII. fig. 3, 6.67); it is a roughly orbicular plate of cartilage notched in front 
and on each side; and the Jeft side is the larger of the two. 
The first branchial arch has lost its upper element; there is only an unossified cerato- 
branchial (c.dr1), an arcuate, solid, thickish rod, hooked inwards above. 
The second arch is one fourth larger; but it has two parts—an epi- and a cerato- 
branchial (c.07’, e.7°), marked out by extensive ossification ; as phalangiform bony bars, 
united by cartilage; the upper segment is a little less than the lower. 
Recapitulation of the Cranial Elements of Sieboldia, and Comparison with Menopoma. 
As the description of the skull of Menopoma comes next, and as these two skulls 
1 T am not sure that the segment here called “ epihyal” does not answer to the “interhyal” of Fishes ; 
if so, then the styloid end of the “ cerato-hyal “ would be the non-segmented “ epihyal.” 
