the cleithrum and posterodoreally with the postcleith- 

 rum. Anteriorly the medial edge of the supracleithrum 

 articulates by fibrous tissue with the entire length of the 

 dorsolateral surface of the pterotic and with the postero- 

 lateral edge of the sphenotic. 



Cleithrum. —Widest dorsally, constricted at the 

 level of the scapula and becoming a thin flat plate ven- 

 trally. Above the level of the scapula, the posterior region 

 of the medial surface of the cleithrum articulates by 

 fibrous tissue dorsolaterally with the broadly overlying 

 supracleithrum, while the dorsal edge of the portion of 

 the cleithrum overlain by the supracleithrum articu- 

 lates with the anteroventral edge of the postcleithrum. 

 Along its posterior edge the cleithrum possesses a broad 

 but shallow concavity in which the anterodorsal edge of 

 the scapula is held by fibrous tissue. The posterior edge 

 of the cleithrum below the scapula articulates by fibrous 

 tissue with the anterior edge of the coracoid. The ventro- 

 medial surfaces of the two cleithra articulate with one 

 another by fibrous tissue. 



Postcleithrum. — Approximately Y-shaped; with 

 the bifurcate portion at the level of the actinosts and the 

 long arm articulated by fibrous tissue anterolaterally 

 with the supracleithrum and anteroventrally with the 

 cleithrum. In neither of the two cleared and stained spec- 

 imens is there any evidence of the postcleithrum being 

 composed of two elements, the dorsal and ventral post- 

 cleithra apparently having fused into a single piece. The 

 lateral surface of the portion of the postcleithrum that 

 lies posterior to the cleithrum is embedded in the thick, 

 firmly collagenous subdermal tissue of the skin. The 

 medial surface of the anterior fork of the inverted Y over- 

 lies and articulates by fibrous tissue with the bases of the 

 three actinosts. 



Coracoid. — A flattened plate throughout its length, 

 except ventrally where it becomes more rounded and 

 shaftlike; slightly expanded anteriorly in the middle 

 region of its length and more expanded anteriorly at its 

 dorsal end; cartilage filled at its anterodorsal edge; artic- 

 ulates anterodorsally through cartilage with the base of 

 the scapula, while its dorsal edge articulates through car- 

 tilage and fibrous tissue with the bases of the three ac- 

 tinosts. The anterior edge of the coracoid articulates by 

 fibrous tissue with the posterior edge of the cleithrum. 



Scapula. — Widest dorsally, constricted in the mid- 

 dle and only becoming slightly expanded ventrally; 

 scapular foramen not entirely enclosed by bone, for the 

 anteroventral edge of the scapula is well separated from 

 the posterior edge of the cleithrum. A sheet of fibrous tis- 

 sue, bearing a small pore representing the scapular fora- 

 men, connects these edges of the scapula and cleithrum. 

 The scapula is deeply cartilage filled at its dorsal and 

 ventral edges. The posterodorsal edge of the scapula is 

 somewhat expanded posteriorly and overlies the antero- 

 dorsal edge of the anteriormost actinost, with which it ar- 

 ticulates by fibrous tissue. The posteroventral edge of the 



scapula articulates by fibrous tissue with the anteroven- 

 tral edge of the anteriormost actinost, while ventrally the 

 scapula articulates through cartilage with the coracoid. 



Actinosts. —Three actinosts present; decreasing in 

 size and degree of central constriction posteriorly in the 

 series. The reduced first actinost of other plectognaths is 

 not present as a separate piece, although it is possible 

 that the posterodorsal portion of the scapula represents 

 the remains of this actinost indistinguishably fused to 

 the scapula. The three actinosts articulate with one 

 another dorsally and ventrally by fibrous tissue and with 

 the coracoid through cartilage and fibrous tissue. The ac- 

 tinosts are cartilage filled at their dorsal and ventral 



Fin rays. — Twelve fin rays present, the first three 

 rays and the last ray unbranched, the others so exten- 

 sively branched distally that up to 20 terminal segments 

 (incomplete quintuple dichotomies) are present on some 

 fin rays. The medial and lateral halves of each fin ray are 

 not closely apposed to one another except distally, a large 

 amount of connective tissue otherwise separating the two 

 halves for most of their lengths. For the vast majority of 

 their lengths the rays lack cross-striations, which are 

 only present extremely distally on some of the branches 

 as poorly defined articulations. The first ray differs from 

 the others by possessing a slender anteroventral process 

 from the anterior edge of the medial half of the fin ray. 

 The deeply bifurcate bases of the rays surround plugs of 

 cartilage whose ventral regions are calcified either as a 

 single piece or as a pair (lateral and medial) of calcifica- 

 tions (not shown in the figures). 



VERTEBRAL COLUMN. —All vertebrae with bicon- 

 cave centra, except for the last, which ends posteriorly 

 with a relatively flat surface. 



Abdominal Vertebrae. 



First vertebra. — Neural spine bifid; no bony roof 

 over the neural canal. The rim of the concave anterior 

 face of the centrum articulates by fibrous tissue with the 

 rim of the concave posterior end of the basioccipital. The 

 anterolateral edges of the bifid neural spine articulate by 

 fibrous tissue with the medial surfaces of the anterodor- 

 sal wings of the basioccipital. The dorsal edges of the 

 bifid neural spine are overlain by the anterior edge of the 

 neural spine of the second vertebra, while its posterolat- 

 eral edges are indented to accommodate the short prongs 

 from the anterolateral edges of the neural spine of the 

 second vertebra. 



Other abdominal vertebrae. — Eight abdominal ver- 

 tebrae in two specimens; neural spines increasing in 

 length from the second to the fifth abdominal vertebrae; 

 neural spines of the fifth to eighth abdominal vertebrae 

 about equal in length; second to eighth abdominal ver- 

 tebrae with bony roofs over the neural canal. The neural 

 arches from either side of the second abdominal verte- 



