Most of the internal differences between the three 

 genera of molids clearly indicate that Mola and 

 Masturus are much more closely related to one another 

 than either is to Ranzania, as widely supposed in the 

 past, mostly on the basis of external appearances. 



In Mola and Masturus the mesopterygoid is a small 

 squarish bone which does not make contact posteriorly 

 with the metapterygoid, while in Ranzania it is larger 

 and more elongate, and contacts the metapterygoid. In 

 Mola and Masturus the epiotics are dome-shaped and 

 only moderately prolonged posterodorsally, while in Ran- 

 zania they are greatly elongate posterodorsally as thin 

 but wide bands of bone. In Mola and Masturus the 

 supraoccipital crest is short and broad, while in Ran- 

 zania it is long and narrow, extending back as far beyond 

 the head to contact the anterior prolongation of the first 

 basal pterygiophore of the dorsal fin. In Mola and Mas- 

 turus the sphenotic only slightly overlies the anterolat- 

 eral surface of the pterotic, while in Ranzania it broadly 

 overlies it. In Mola and Masturus the vomer is ossified, 

 while it is unossified in Ranzania. In Mola and Mastu- 

 rus the basisphenoid is placed in the posterior half 

 of the orbit and articulates with the prootic and ptero- 

 sphenoid as well as with the parasphenoid, while in Ran- 

 zania the basisphenoid is placed in the middle of the or- 

 bit and articulates with the frontals above and the pala- 

 tines and parasphenoid below. In Mola and Masturus the 

 anterodorsal prolongations from either side of the basioc- 

 cipital do not meet one another in the midline above the 

 neural canal, being separated there by the long anterior 

 extension of the neural spine of the first vertebra, while 

 in Ranzania the anterodorsal prolongations of the basioc- 

 cipital meet and fuse or suture in the midline above the 

 neural canal, being only slightly separated from one 

 another posteriorly by the short anterior extension of the 

 neural spine of the first vertebra. In Mola and Masturus 

 there are six branchiostegal rays, the fifth about the 

 same size as the fourth and the sixth much more slender 

 than any of the others, while in Ranzania there are only 

 five branchiostegals, the sixth either being lost or fused 

 with the fifth, which is much larger than any of the other 

 branchiostegals. In Mola and Masturus the cerato- 

 branchials are exceptionally deep bodied, but in Ran- 

 zania they are not. In Mola and Masturus the operculum 

 is shorter and wider than in Ranzania. In Mola and 

 Masturus the suboperculum retains a posterior prolonga- 

 tion behind or below the operculum as well as an ante- 

 rior portion directed internal to the rear of the preoper- 

 culum, while the suboperculum of Ranzania is repre- 

 sented only by the anterior portion, which is longer than 

 in Mola and Masturus. In Masturus the interoperculum 

 is unossified and in Mola it is a short rod well separated 

 from the suboperculum, while in Ranzania it is a long rod 

 which contacts the suboperculum. In Mola and Masturus 

 none of the actinosts are sutured to one another, while in 

 Ranzania all of them are sutured or interdigitated to one 

 another to some extent. In Mola and Masturus the post- 

 cleithrum is not greatly expanded posteriorly as a 

 flattened plate, while it is in Ranzania. In Mola and 

 Masturus the parasphenoid is about as wide anteriorly as 



it is toward the rear of the orbit, while in Ranzania it is 

 narrower anteriorly than more posteriorly. In Mola and 

 Masturus the posterior portion of the palatine articu- 

 lates broadly to the lateral surface of the parasphenoid, 

 while in Ranzania it articulates more to the dorsal sur- 

 face of the parasphenoid. In Mola and Masturus the 

 symplectic is of moderate length, extending back poste- 

 riorly only about half the length of the ventral edge of the 

 metapterygoid, while in Ranzania it is elongate and ex- 

 tends back nearly the whole length of the ventral edge of 

 the metapterygoid. In Mola and Masturus the neural 

 arch and spine of the second vertebra is prolonged ante- 

 riorly and posteriorly well beyond the levels of the ante- 

 rior and posterior edges of the centrum, while in Ran- 

 zania they are not prolonged. In Mola and Masturus the 

 neural arches of the abdominal vertebrae are not inter- 

 digitated with one another, while in Ranzania they are 

 broadly and deeply interdigitated. In association with 

 their deeper bodies, the basal pterygiophores of the dor- 

 sal and anal fins in Mola and Masturus are less elongate, 

 and the neural and haemal spines and the pterygio- 

 phores they support are less obliquely placed than in 

 Ranzania. In Mola and Masturus only the first two 

 haemal spines of the caudal vertebrae are decidedly 

 oriented toward one another, while in Ranzania most of 

 the successive sets of two haemal spines from the caudal 

 vertebrae are decidedly oriented toward one another. 

 The first basal pterygiophore of the dorsal fin is a rela- 

 tively simple shaft in Mola and Masturus, and it is 

 broadly in contact with the second basal pterygiophore, 

 while in Ranzania the first basal pterygiophore is a com- 

 plex element obviously representing the fusion of two 

 basal pterygiophores, and it is not in contact with the se- 

 cond basal pterygiophore. A short but deep supraneural 

 is present in Mola, but the similarly shaped region 

 anterodorsally on the first basal pterygiophore of the dor- 

 sal fin in the single specimen of Masturus studied is fully 

 fused to the pterygiophore. In Ranzania the long ante- 

 rior extension from the complex first basal pterygio- 

 phore may represent a supraneural fully fused to the 

 pterygiophore. In Mola and Masturus the posterior sur- 

 face of the proximal end of the first basal pterygiophore 

 of the anal fin is deeply concave and encloses the distal 

 end of the haemal spines of the first two caudal 

 vertebrae, while in Ranzania this pterygiophore is not 

 concave proximally and articulates along the anterior 

 edge of the haemal spine of the first caudal vertebra. In 

 Mola and Masturus most of the basal pterygiophores of 

 the dorsal and anal fins are anteroposteriorly expanded 

 and platelike, while in Ranzania they are mostly long 

 slender rods. In Mola and Masturus the bases of the first 

 dorsal and anal fin rays are only slightly, if at all, larger 

 than those just behind them, while in Ranzania these 

 bases are greatly enlarged anteriorly. In Mola and 

 Masturus the ossification of the skeleton is less complete 

 than in Ranzania. 



In only a few ways are either Mola or Masturus more 

 like Ranzania than one another. The trituration teeth in 

 the upper jaw of all three genera occur as a single series of 

 elongate teeth to either side of the midline. In the lower 



