83 



the tail, showing the arrangement of the enameled or ganoid osseous scales. 

 Tlii>-i- which form tin- lateral line are perforated by the mucous ducts. 



JV- Willoughby : PMC. lab. P. ./. 2. from this specimen. Bloch, IcAtk. vi. /./. 390. 

 Habitat. The lakes ami riven of the wanner parts of North America. 

 This specimen was formerly preserved in the Museum of the Royal Society at (iresham 

 College. 



Mia. Brit. 



872. The dried skin of a Lepidonleu*, showing the unsymmetrical or heterocercal form 

 of tail. Roth this fonn of tail and the structure of the scales arc extremely 

 rare in existing fishes, the Jsepidotteu* being the only existing genus of osseous 

 fishes which is known to combine them. But the characters arc very common 

 amongst extinct fishes, especially those of the older secondary formations. 



fttrchated. 



Family Sturionida. 



373. The mutilated skull of the Paddle-fish (P/anirostra Spatula). 



It is remarkable for the rostral prolongation of the nasal and vomeriue bones, the rostrum 

 being flattened horizontally and expanded like the mandibles of a Spoon-bill. The sides of 

 the rostrum are strengthened by a reticulate disposition of bony matter in the form of stars, 

 the rays of which anastomose. The upper part of the cranium is also imperfectly ossified. 

 There is a long vacuity between the frontal, parietal, postfrontal and mastoid bones : the 

 tympanic pedicle is a simple elongated piece of bone expanded at both ends. Tin- mandi- 

 bular and hyoidean arches an* suspended by a short cartilage to the end of the tympanic 

 bone: the palatines are extremely small. The prr maxillary and maxillary bones seem to 

 hare coalesced ; they expand as they extend backwards to become attached to the cartilage 

 supporting the mandibular arch. The slightly ossified pterygoids run |>arallel with them 

 along the inner sides to the same part. The articular and dentary pieces of the lower jaw 

 hare coalesced, but there is a trace of a slender splenial piece on the inner side of the man- 

 dible. All the bones of the mouth are edentulous, but the membrane covering the extre- 

 mities of the upper and lower jaw is roughened bv extremely minute denticles in the recent 

 fish. The ceratohyals are partially ossified : the rest of the hyoidean arch is cartilaginous. 

 A branchiostegal appendage in the form of an irregular elongated flattened bone, resolved 

 posteriorly into osseous fibres, extends from each side of the commencement of the hyoidean 

 arch. A similar but larger opercular appendage extends backwards from the extremity of the 



tympanic pedicle. 



Presetted by Prof. Oven, F.Jt.S. 



374. The skull of a Sturgeon (Acipnter Sturio). 



The suprascapular dermal plate is supported by a distinct cartilage of a subtrihedral form, 

 with the angles of its base slightly produced and articulated by ligament, the one to the end 



M 2 



